security/vboot: Include fspt.bin in the RO region only

fspt.bin is run before verstage so it is of no use in RW_A/B.

Change-Id: I6fe29793fa638312c8b275b6fa8662df78b3b2bd
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/52853
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Michał Żygowski <michal.zygowski@3mdeb.com>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/security/vboot/Makefile.inc

@@ -187,6 +187,7 @@ regions-for-file = $(subst $(spc),$(comma),$(sort \
 		cmos.default \
 		intel_fit \
 		intel_fit_ts \
+		fspt.bin \
 		$(call strip_quotes,$(CONFIG_RO_REGION_ONLY)) \
 		,$(1)),COREBOOT,\
 		$(if $(filter \