northbridge/intel/gm45/gma: Add backlight control register field

This allows the backlight control register to be set via devicetree.cb

Change-Id: I32b42dfc1cc609fb6f8995c6158c85be67633770
Signed-off-by: Timothy Pearson <tpearson@raptorengineeringinc.com>
Reviewed-on: http://review.coreboot.org/9330
Tested-by: build bot (Jenkins)
2 files changed