Add function needed to generate ACPI backlight control SSDT, along with
Kconfig values for accessing the registers.
Tested by adding gfx register on google/magpie. Backlight controls
work on Windows 10 and Linux 6.1.
Change-Id: Iaa9872cd590c3b1298667cc80354ed3efd91c6c8
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74324
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Sean Rhodes <sean@starlabs.systems>