postcar: Add cbmem_stage_cache

S3 resume path executing through postcar was unable
to utilise cached ramstage in CBMEM.

Change-Id: Icc8947c701ca32b4f261ebb78dfc1215b7ed2da0
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/21382
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/lib/Makefile.inc

@@ -179,6 +179,7 @@ postcar-y += ext_stage_cache.c
 else
 ramstage-$(CONFIG_RELOCATABLE_RAMSTAGE) += cbmem_stage_cache.c
 romstage-$(CONFIG_RELOCATABLE_RAMSTAGE) += cbmem_stage_cache.c
+postcar-$(CONFIG_RELOCATABLE_RAMSTAGE) += cbmem_stage_cache.c
 endif