soc/intel/apollolake: Add romstage that calls FSP2.0 driver

This romstage is minimalistic. Its goal is to set up some BARs
that FSP expects to be set and then invoke FSP driver to train
memory.

Change-Id: I3fa56aafe99cf6cf062a46dece3a0febeafdbfad
Signed-off-by: Andrey Petrov <andrey.petrov@intel.com>
Reviewed-on: https://review.coreboot.org/13805
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/intel/apollolake/Makefile.inc

@@ -17,6 +17,7 @@ bootblock-y += tsc_freq.c
 bootblock-$(CONFIG_SOC_UART_DEBUG) += uart_early.c
 
 romstage-y += placeholders.c
+romstage-$(CONFIG_PLATFORM_USES_FSP2_0) += romstage.c
 romstage-y += gpio.c
 romstage-$(CONFIG_SOC_UART_DEBUG) += uart_early.c
 romstage-y += mmap_boot.c