Linux's own r8169 through LDLS, deep idle, and the GPU plan

The RTL8168 is now driven by Linux's r8169, unmodified, in a process.
`make ldls-r8169` stages it from the running kernel together with libphy,
mdio-bus, mdio_devres and the Realtek PHY driver, the kernel's BTF and
the RTL PHY firmware, and etc/schinit/ldls-r8169.job starts it at boot
with its log in /var/log/ldls-r8169.log. The native driver is out of the
registry; its code, now with Linux's 8168H setup, stays as the fallback.

LDLS grows what that needed:
- ldlsd loads a comma-separated module set in dependency order, each
  linking against the ones before it, with BTF read before any
  init_module runs;
- a driver core (bus match, driver probe), devres, kernel printf, real
  udelay/msleep/ktime and 1000 Hz jiffies, phylib's bitmaps and
  link_mode_params, firmware from /lib/firmware, and the symbols whose
  stub zero was a lie (list validity, try_module_get, dev_err_probe,
  eth_platform_get_mac_address);
- pdev->bus is a real pci_bus, and cmovcc from per-CPU memory is
  rewritten like the other %gs forms.
In QEMU all five modules load, link and initialise, and r8169 registers
and finds no device. Probe and traffic are untested until real hardware.

The kernel turns ASPM off on Realtek NIC links at boot, as r8169 does
through pci_disable_link_state, which a process cannot.

Idle CPUs enter ACPI _CST's C2 (CC6 on Zen) by port read or MWAIT when
the APIC timer keeps running, instead of only ever halting at C1.

docs/plan/gpu.md: amdgpu and nouveau through LDLS, with measurements.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4

ldls/stub.h

@@ -35,6 +35,9 @@ struct stubs {
 //
 // `code` has to be executable memory; this only writes the bytes.
 void stub_build(struct stubs *s, unsigned char *code, int n);
+// The same, numbering the stubs from `first`: with several modules loaded,
+// each module's stubs follow the previous module's in one shared name table.
+void stub_build_from(struct stubs *s, unsigned char *code, int n, int first);
 
 // The address of stub `i`, to hand to the loader as a symbol value.
 unsigned long long stub_addr(const struct stubs *s, int i);