mb/google/brya/var/volmar: Disable PCH USB2 phy power gating

The patch disables PCH USB2 Phy power gating to prevent possible display
flicker issue for kano board. Please refer Intel doc#723158 for
more information.

BUG=None
TEST=Verify the build for volmar board

Signed-off-by: Ren Kuo <ren.kuo@quanta.corp-partner.google.com>
Change-Id: I4d12f7214a306ded54b4536a27fe0fb7f3c33b8b
Reviewed-on: https://review.coreboot.org/c/coreboot/+/65307
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
diff --git a/src/mainboard/google/brya/variants/volmar/overridetree.cb b/src/mainboard/google/brya/variants/volmar/overridetree.cb
index 8ebb94c..aca32f8 100644
--- a/src/mainboard/google/brya/variants/volmar/overridetree.cb
+++ b/src/mainboard/google/brya/variants/volmar/overridetree.cb
@@ -23,6 +23,10 @@
 chip soc/intel/alderlake
 	register "sagv" = "SaGv_Enabled"
 
+	# As per Intel Advisory doc#723158, the change is required to prevent possible
+	# display flickering issue.
+	register "usb2_phy_sus_pg_disable" = "1"
+
 	register "tcss_aux_ori" = "1"
 	register "typec_aux_bias_pads[0]" = "{.pad_auxp_dc = GPP_E22, .pad_auxn_dc = GPP_E23}"