mb/google/brya/var/agah: Add GPU power sequencing

mb/google/brya/var/agah: Add GPU power sequencing

This patch adds support for power sequencing of the Nvidia GN3050 for
agah, which uses PCH GPIOs to control the 5 power rails required for
the GPU. The GPU is power sequenced on during mainboard
initialization, then it is enumerated on the PCI bus and its resources
are assigned. This GPU will be used in a sort of "hybrid graphics"
mode, therefore during finalization, since its PCI BARs are saved into
ACPI memory and the GPU is not required upon initial boot, the GPU is
power sequenced off.

Signed-off-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Change-Id: I1072be12ef58af5859e2a2d19c4a9c1adc0b0f88
Reviewed-on: https://review.coreboot.org/c/coreboot/+/62384
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>