mb/google/skyrim: Enable SPL fusing on frostflow

Enable Frostflow platform to send the fuse SPL (security patch level)
command to the PSP.

BUG=b:274028833
BRANCH=none
TEST=FW_NAME="frostflow" emerge-skyrim coreboot chromeos-bootimage
Then get "PSP: SPL Fusing Update Requested." in the firmware log.

Change-Id: I6437d5324877702f2f8b4c69d4c850543e1b74be
Signed-off-by: Frank Wu <frank_wu@compal.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/73884
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>

src/mainboard/google/skyrim/Kconfig

@@ -86,6 +86,7 @@ config SPL_RW_AB_TABLE_FILE
 
 config SOC_AMD_COMMON_BLOCK_PSP_FUSE_SPL
 	default y if BOARD_GOOGLE_WINTERHOLD
+	default y if BOARD_GOOGLE_FROSTFLOW
 	default n
 
 config FMDFILE