arch/x86: provide verstage support for CONFIG_C_ENVIRONMENT_BOOTBLOCK

When CONFIG_C_ENVIRONMENT_BOOTBLOCK is employed there's no need for
a chipset specific verstage entry point because cache-as-ram has
already been initialized. Therefore, provide a default entry point
for verstage in that environment.

Change-Id: Idd8f45bd58d3e5b251d1e38cca7ae794b8b77a28
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/14971
Tested-by: build bot (Jenkins)
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Andrey Petrov <andrey.petrov@intel.com>

src/arch/x86/Makefile.inc

@@ -178,6 +178,10 @@ verstage-y += memset.c
 verstage-y += memcpy.c
 verstage-y += memmove.c
 verstage-$(CONFIG_X86_TOP4G_BOOTMEDIA_MAP) += mmap_boot.c
+# If C environment is used for bootblock it means there's no need
+# for a chipset-specific car_stage_entry() so use the generic one
+# which just calls verstage().
+verstage-$(CONFIG_C_ENVIRONMENT_BOOTBLOCK) += verstage.c
 
 verstage-$(CONFIG_COLLECT_TIMESTAMPS) += timestamp.c