Gru: Increase bit-per-pixel to 32

This enhances gradation of some icons on vboot screens.

BUG=chrome-os-partner:56056
BRANCH=none
TEST=Booted kevin-tpm2

Change-Id: I2fc943f89386ccc6cd9293f5811182a5a51d99b0
Signed-off-by: Martin Roth <martinroth@chromium.org>
Original-Commit-Id: bb1f0fb00d023c045305edc6c9fc655b764a4e8c
Original-Change-Id: Ieb61830b9555da232936087cdcf7c61a1e55bab4
Original-Signed-off-by: Daisuke Nojiri <dnojiri@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/376883
Original-Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/16579
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
diff --git a/src/mainboard/google/gru/devicetree.cb b/src/mainboard/google/gru/devicetree.cb
index be1d4660..7a421b2 100644
--- a/src/mainboard/google/gru/devicetree.cb
+++ b/src/mainboard/google/gru/devicetree.cb
@@ -17,5 +17,5 @@
 	device cpu_cluster 0 on end
 	register "vop_id" = "0"
 	register "vop_mode" = "VOP_MODE_EDP"
-	register "framebuffer_bits_per_pixel" = "16"
+	register "framebuffer_bits_per_pixel" = "32"
 end