mb/google/trulo/var/uldrenite: Enable DPTF oem_variables

Support oem_variables and change based on EC notify event.

BUG=b:394177292
BRANCH=firmware-trulo-15217.771.B
TEST=emerge-nissa coreboot

Change-Id: Iac18cb968906a9dfe53836432ba8dbefee1dcc8e
Signed-off-by: John Su <john_su@compal.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/86394
Reviewed-by: Dtrain Hsu <dtrain_hsu@compal.corp-partner.google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kapil Porwal <kapilporwal@google.com>
Reviewed-by: Eric Lai <ericllai@google.com>

src/mainboard/google/brya/variants/uldrenite/include/variant/ec.h

@@ -5,4 +5,7 @@
 
 #include <baseboard/ec.h>
 
+/* Enable DPTF OEM variable */
+#define DPTF_ENABLE_OEM_VARIABLES
+
 #endif

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

@@ -225,7 +225,11 @@ chip soc/intel/alderlake
 					[3] = {   8,  500 }
 				}"
 
-				device generic 0 on end
+				register "oem_data.oem_variables" = "{
+						[0] = 0x0
+				}"
+
+				device generic 0 alias dptf_policy on end
 			end
 		end # DPTF
 		device ref tcss_xhci on