haswell: Update GT PM register value

This was changed to 0x80000000 in SA BWG 1.5.0.

Change-Id: Ic6773f45057f3eb93b2d93ee543e3db77fccf805
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/50852
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/4166
Tested-by: build bot (Jenkins)
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
diff --git a/src/northbridge/intel/haswell/gma.c b/src/northbridge/intel/haswell/gma.c
index e577fb5..f3ddbd3 100644
--- a/src/northbridge/intel/haswell/gma.c
+++ b/src/northbridge/intel/haswell/gma.c
@@ -124,7 +124,7 @@
 	gtt_write(0x12054, 0x0000000a);
 	gtt_write(0x22054, 0x0000000a);
 
-	gtt_write(0x0a008, 0x10000000);
+	gtt_write(0x0a008, 0x80000000);
 	gtt_write(0x0a024, 0x00000b92);
 
 	/* Enable RC6 in idle */