intel post-car: Consolidate choose_top_of_stack()

Change-Id: I2c49d68ea9a8f52737b6064bc4fa703bdb1af1df
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/15463
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/lib/Makefile.inc

@@ -78,6 +78,7 @@ romstage-$(CONFIG_PRIMITIVE_MEMTEST) += primitive_memtest.c
 ramstage-$(CONFIG_PRIMITIVE_MEMTEST) += primitive_memtest.c
 romstage-$(CONFIG_CACHE_AS_RAM) += ramtest.c
 romstage-$(CONFIG_GENERIC_GPIO_LIB) += gpio.c
+romstage-y += romstage_stack.c
 romstage-y += stack.c
 ramstage-y += rtc.c