boot/uefi: the system information panel, and the offset that faked a version

ui_panel was written for this screen during the loader restyle and then
never called -- dead code sitting in boot/common/ui.c waiting for the row
that would use it. This is that row: F8 -> System Information, showing
firmware vendor and revision, UEFI revision, CPU brand, usable memory,
current mode and whether ACPI was found.

Everything is read when the screen is drawn rather than captured at
startup, because the resolution row above it can have changed the mode,
and a panel still reporting what the machine booted with is worse than no
panel at all.

Two facts are deliberately read through the same code that feeds the
kernel -- efi_type_to_e820() for what counts as usable memory, and
find_rsdp() for ACPI. A panel with its own idea of either would be a
second implementation to keep in step, and the ACPI line exists precisely
because a missing RSDP means no MADT, no IOAPIC and no SMP, which has
already been debugged once from the far end.

The screenshot caught a bug in the screen it was taken to verify: UEFI
revision read "21587.2286". EFI_TABLE_HEADER begins with a UINT64
Signature, so Revision is at offset 8 and I had read offset 4 -- the
upper half of "IBI SYST", formatted as a version number. It now reads 2.7
under OVMF, which is correct.

Verified by driving the menu over the QEMU monitor and reading the
pixels: five rows with the hint updated to 1-5, the panel centred, and
every value cross-checkable -- EDK II, firmware 1.0, UEFI 2.7, "QEMU
Virtual CPU version 2.5+" against -cpu qemu64, 1018 MB of the 1 GB given,
1280x800 matching what fbshot captures, ACPI present. The highlight sits
9 px inside both panel borders, symmetric.

F8 has a 1.5 s window, so the capture presses it repeatedly through boot
rather than guessing when OVMF finishes -- and only F8, since any other
key breaks the wait and boots.

Also: every ESP drive now says format=raw. QEMU warned about probing the
format on each of the fifteen or so places that attach it, which is new
noise on what is now the only boot path. 110 [ok], no failures, no
warnings.

tools/posix/schcom_test.sh

@@ -46,7 +46,7 @@ EOF
       -machine pc-i440fx-9.2 -cpu qemu64,+rdtscp \
       -drive if=pflash,format=raw,unit=0,readonly=on,file=build/OVMF_CODE.fd \
       -drive if=pflash,format=raw,unit=1,file=build/schcom-OVMF_VARS.fd \
-      -drive file=fat:rw:build/esp,index=0,media=disk \
+      -drive file=fat:rw:build/esp,index=0,media=disk,format=raw \
       -drive file=build/schfs.img,format=raw,index=1,media=disk \
       -m 1G -smp 1 \
       -display none -vga std \