drivers/intel/gma: Drop unused `backlight` field

Change-Id: I9d7f8337653f93f40550a3d2886fe7b3845eac69
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/39879
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/drivers/intel/gma/i915.h

@@ -88,7 +88,6 @@ u32 gtt_read(u32 reg);
 struct i915_gpu_controller_info
 {
 	int use_spread_spectrum_clock;
-	u32 backlight;
 	int ndid;
 	u32 did[5];
 };