mb/google/volteer: Enable D3HotEnable and D3ColdEnable for Volteer

This explicitly enables both of TCSS D3HotEnable and D3ColdEnable
from Volteer devicetree.cb setting.

BUG=:b:146624360
TEST=Built and booted on Volteer.

Signed-off-by: John Zhao <john.zhao@intel.com>
Change-Id: I1a168ad87169c0f6633704c55c9293aa25710188
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41547
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Wonkyu Kim <wonkyu.kim@intel.com>
diff --git a/src/mainboard/google/volteer/variants/baseboard/devicetree.cb b/src/mainboard/google/volteer/variants/baseboard/devicetree.cb
index 6933695..02060bd 100644
--- a/src/mainboard/google/volteer/variants/baseboard/devicetree.cb
+++ b/src/mainboard/google/volteer/variants/baseboard/devicetree.cb
@@ -136,6 +136,10 @@
 	register "IomTypeCPortPadCfg[7]" = "0x0"
 
 
+	# D3Hot and D3Cold for TCSS
+	register "TcssD3HotEnable" = "1"
+	register "TcssD3ColdEnable" = "1"
+
 	# DP port
 	register "DdiPortAConfig" = "1"	# eDP
 	register "DdiPortBConfig" = "0"