mb/google/wyvern: use SaGv_FixedHigh

No need for dynamic config (and the additional RAM training time)
on a Chromebox; always use high power/high performance mode.

Change-Id: I8ad773d1c616b746235ec67b98b83c5910464140
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/58230
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/mainboard/google/hatch/variants/wyvern/overridetree.cb

@@ -20,6 +20,10 @@ chip soc/intel/cannonlake
 		[PchSerialIoIndexUART2] = PchSerialIoDisabled,
 	}"
 
+	# No need for dynamic config (and the additional RAM training time)
+	# on a Chromebox; always use high power/high performance mode
+	register "SaGv" = "SaGv_FixedHigh"
+
 	# USB configuration
 	register "usb2_ports[0]" = "{
 		.enable = 1,