Add AppleT2Smc module: Apple T2 SMC over MMIO

[golirt1]

Adds a module for the SMC on 2018–2020 Intel Macs with the Apple T2 chip.

On those machines the T2 intercepts the legacy SMC I/O-port protocol
(0x300/0x304), so the usual port handshake returns garbage under Windows. The T2
instead exposes the SMC through an MMIO window at physical 0xFE0B0000.

The module maps that window with io_space_map and performs the SMC
request/response handshake in kernel mode, exposing only SMC operations — it
never exposes raw physical memory access:

• ioctl_smc_read — READ (0x10), GET_KEY_BY_INDEX (0x12), GET_KEY_TYPE (0x13)
• ioctl_smc_write — WRITE (0x11)

Writes are restricted by an allowlist to fan-control keys only (F<n>Tg,
F<n>Md, FS! ), so the module can't be used to poke arbitrary SMC state —
only fan speed/mode, which is its purpose. main() probes FNum and refuses to
load (STATUS_NOT_SUPPORTED) if the SMC doesn't respond, so it won't touch this
physical range on non-Apple hardware.

Register offsets, access widths (control registers are 32-bit writes;
status/length/error are byte reads; the data buffer is byte-addressed), the
completion-status bit (0x20) and the exponential backoff mirror the Linux T2
applesmc driver (MCMrARM/mbp2018-etc, applesmc_t2_kmod.c). GET_KEY_TYPE's
special MMIO result layout (type@0, datalen@5, flags@6) is repacked into the
conventional [len, type, flags] form.

Compiles cleanly with the repo CI. I'd appreciate a review of the access widths
and the write allowlist in particular. Thanks!