baytrail: Enable GFX device

- Ungate display in PUNIT
- Set GSM to 64MB since 32MB is not supported in <C0 stepping
- Initialize power management registers in GTT
- Execute VBIOS if found

BUG=chrome-os-partner:23507
BRANCH=rambi
TEST=build and boot to dev screen via HDMI on rambi

Change-Id: Idb032c7ea7f16b651b4c921e3429a652fe663a5d
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/174922
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/4907
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/soc/intel/baytrail/Makefile.inc

@@ -18,6 +18,7 @@ romstage-$(CONFIG_CACHE_MRC_SETTINGS) += mrc_cache.c
 ramstage-y += spi.c
 smm-y += spi.c
 ramstage-y += chip.c
+ramstage-y += gfx.c
 ramstage-y += iosf.c
 romstage-y += iosf.c
 ramstage-y += northcluster.c