mb/google/brox/var/lotso: Add fw_config field for storage

Add STORAGE_UNKNOWN, STORAGE_UFS, STORAGE_NVME for storage fw_config
field to prevent depthcharge build break.

BUG=b:333494257
TEST=emerge-brox coreboot depthcharge sys-boot/chromeos-bootimage

Change-Id: Idb62e3f37e1480979ae529692455beb533434520
Signed-off-by: tongjian <tongjian@huaqin.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82056
Reviewed-by: Kun Liu <liukun11@huaqin.corp-partner.google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Eric Lai <ericllai@google.com>

src/mainboard/google/brox/variants/lotso/overridetree.cb

@@ -1,3 +1,11 @@
+fw_config
+	field STORAGE 0 1
+		option STORAGE_UNKNOWN			0
+		option STORAGE_UFS			1
+		option STORAGE_NVME			2
+	end
+end
+
 chip soc/intel/alderlake
 
         device domain 0 on