mb/google/guybrush: Fix SMMSTORE size, alignment

SMMSTOREv2 requires 64k min size, 64k alignment.

TEST=build guybrush with SMMSTOREv2 enabled

Change-Id: I78cb873a5634c659067367260cc7063fbd60d77a
Signed-off-by: Matt DeVillier <matt.devillier@amd.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/68123
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/mainboard/google/guybrush/chromeos.fmd

@@ -18,7 +18,7 @@ FLASH@0xFF000000 16M {
 		}
 		RW_VPD(PRESERVE) 8K
 		RW_NVRAM(PRESERVE) 20K
-		SMMSTORE(PRESERVE) 4K
+		SMMSTORE(PRESERVE)@0x620000 64K
 		RW_LEGACY(CBFS)
 		WP_RO@8M 8M {
 			RO_VPD(PRESERVE) 16K