gfx: the console and the crash screen stop drawing on a driver by name

Same disease as the network stack, one subsystem over. kernel/dev/vga.c
was three things wearing one name: the owner of the framebuffer, a
bitmap drawing library, and the text console. Only the first is a
driver, and because they shared a file they shared a prefix -- so
panic.c drew the crash screen with vga_fill_rect, console.c printed with
vga_putc, /dev/fb0 handed out vga_fb_phys, and every one of those files
named a display driver it had no business knowing about.

Split three ways:

  - kernel/drivers/gpu/vga/vga_fb.c owns the VBE framebuffer -- the mode
    the loader programmed and handed over, the aperture, and the display
    class vtable. It is a driver and now lives with the driver that
    finds the card on the bus.
  - kernel/dev/gfx.c draws: pixels, shapes, glyphs, the cursor, scroll,
    the ANSI erase operations. It names no driver. The framebuffer
    arrives through gfx_attach_scanout(), so a driver publishes what it
    owns and this file draws on it without knowing what it is.
  - include/gfx.h is the interface, and says why it is deliberately not
    the display class: that one is about frames -- acquire, present,
    vblank -- and the crash screen has to work when nothing else does.

main() no longer calls a display driver. platform_register_devices()
takes the framebuffer address and brings up whatever owns it, which is
where driver names belong; kernel/drivers/registry.c is the file whose
entire job is naming every driver in the kernel.

virtio-gpu got the e1000 treatment as well: instances in an array, the
instance hung on dev->priv by an `attached` hook, and every op reading
it rather than a file-static. It refused the second adapter outright
before, which is not hypothetical -- integrated plus discrete is an
ordinary laptop. The VGA driver deliberately has no such hook, and says
so: there is one framebuffer the loader programmed however many
VGA-class controllers the bus turns up, and a second one publishing the
same scanout is the truth rather than a bug.

Private headers moved next to their drivers: include/virtio.h and
include/xhci.h each had exactly one includer. include/ is for headers
the rest of the kernel needs.

Deleted rather than moved: consoleinit() programmed the sixteen ANSI
colours into the VGA DAC and disabled text-mode blink, by writing ports
0x3C0-0x3C9 from the console. The comment three lines above the colour
table already said this does nothing in a 32bpp linear mode -- there is
no palette to index -- so it was both dead and in the wrong file.

Verified, and this is a refactor so the evidence is that nothing moved:
  - bootcheck -Fb -Net: 59 [ok], no failures. That covers the console
    through every command, /dev/fb0's geometry, writing pixels through
    write() and mapping the framebuffer through mmap.
  - make crashshot: the crash screen renders exactly as before --
    shapes, glyphs, logo and QR code -- which is the whole of gfx.c
    exercised at once, in a panic, with the scanout attached by a driver.
  - make schcom-test: five pixel assertions from the host oracle still
    pass, so the display class and the compositor above it are unmoved.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

kernel/drivers/registry.c

@@ -99,10 +99,17 @@ usb_bind_all(struct usb_dev *dev)
 // is visible in one place, which is the same reasoning as the driver arrays
 // above.
 void
-platform_register_devices(void)
+platform_register_devices(uint64 fb_addr)
 {
   struct device *d;
 
+  // The framebuffer first, before anything that might want to draw. It is a
+  // driver call, and this file is where driver names belong -- main() used to
+  // call vga_init() directly, which put one display driver's name in the
+  // kernel's startup path and would have needed editing to boot on a machine
+  // whose framebuffer came from anywhere else.
+  vga_fb_init(fb_addr);
+
   if ((d = device_add("kbd", DEVBUS_PLATFORM, DEVCLASS_INPUT, "ps2kbd")))
     device_set_desc(d, "PS/2 keyboard");
   if ((d = device_add("mouse", DEVBUS_PLATFORM, DEVCLASS_INPUT, "ps2mouse")))