mb/gigabyte/ga-{h61m-s2pv,b75m-d3h,b75m-d3v}: Clean up mainboard code

I ported ga-h61m-s2pv based on the two Gigabyte b75m boards.
Based on another mainboard's code review comments, this patch
improves the code quality of these three similar boards.

ga-h61m-s2pv is tested and confirmed to be working, but I cannot
say the same regarding the other two mainboards as I do not have them.

Change-Id: Ib7747cceb5ba56f791677204cdc4c54c129c70c3
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/27211
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
diff --git a/src/mainboard/gigabyte/ga-b75m-d3h/devicetree.cb b/src/mainboard/gigabyte/ga-b75m-d3h/devicetree.cb
index 3659354..b0c58f9 100644
--- a/src/mainboard/gigabyte/ga-b75m-d3h/devicetree.cb
+++ b/src/mainboard/gigabyte/ga-b75m-d3h/devicetree.cb
@@ -1,7 +1,7 @@
 chip northbridge/intel/sandybridge
 	# IGD Displays
 	register "gfx.ndid" = "3"
-	register "gfx.did" = "{ 0x80000100, 0x80000240, 0x80000410, 0x80000410, 0x00000005 }"
+	register "gfx.did" = "{ 0x80000100, 0x80000240, 0x80000410 }"
 
 	device cpu_cluster 0 on
 		chip cpu/intel/socket_LGA1155