nb/intel/sandybridge: Drop unnecessary gma.h

It only contains prototypes for the long-gone native graphics init.

Tested with BUILD_TIMELESS=1, Lenovo ThinkPad X230 remains identical.

Change-Id: I9413abb8e49496ada60dcdf801a1f8a03be38d2e
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/45360
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/northbridge/intel/sandybridge/gma.c

@@ -16,7 +16,6 @@
 
 #include "chip.h"
 #include "sandybridge.h"
-#include "gma.h"
 
 struct gt_powermeter {
 	u16 reg;