mb/google/brya/var/banshee: Enable SaGv

Enable SaGv support for Banshee

BUG=b:233930777, b:233703655
BRANCH=firmware-brya-14505.B
TEST=FW_NAME=banshee emerge-brya coreboot chromeos-bootimage

Signed-off-by: Frank Wu <frank_wu@compal.corp-partner.google.com>
Change-Id: I22810f422e3f1d6dd1f64d93e6d7aff5593ff739
Reviewed-on: https://review.coreboot.org/c/coreboot/+/64674
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
Reviewed-by: Ian Feng <ian_feng@compal.corp-partner.google.com>

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

@@ -1,4 +1,6 @@
 chip soc/intel/alderlake
+	register "sagv" = "SaGv_Enabled"
+
 	# Intel Common SoC Config
 	#+-------------------+---------------------------+
 	#| Field             |  Value                    |