drvs/intel/gma/acpi: Add methods to use MBOX3

* Add Mailbox 3 driver
* Request brightness change through Mailbox 3
* Return Ones on error or if unsupported
* Mark existing code as legacy
  (still required if no GMA driver is running)
* Call legacy code if Mailbox 3 is unsupported, on error or
  if gma driver isn't running

Tested on Lenovo T430:
* Brightness control still works
* Brightness is the same on S3 resume

Change-Id: I51554c819148336b204d28972cbf775a10c3fb8a
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-on: https://review.coreboot.org/27711
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-by: Nathaniel Roach <nroach44@gmail.com>
Reviewed-by: Nicola Corna <nicola@corna.info>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>

0 files changed, 0 insertions, 0 deletions