mb/google/brya/var/omnigul: Disable Tccold Handshake

The patch disables Tccold Handshake to prevent possible display
flicker issue for Omnigul board. Please refer to Intel doc#723158
for more information.

BUG=b:279539826
BRANCH=firmware-brya-14505.B
TEST=Verify the build for Omnigul board

Change-Id: I04e54df5afe09c12e1cf774445d57e13ffd8819e
Signed-off-by: Dtrain Hsu <dtrain_hsu@compal.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74737
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Subrata Banik <subratabanik@google.com>

src/mainboard/google/brya/variants/omnigul/overridetree.cb

@@ -10,6 +10,10 @@ 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 "disable_dynamic_tccold_handshake" = "true"
+
 	# Intel Common SoC Config
 	#+-------------------+---------------------------+
 	#| Field             |  Value                    |