driver/intel/fsp2.0: Add External stage cache region helper

If ramstage caching outside CBMEM is enabled
i.e CONFIG_CACHE_RELOCATED_RAMSTAGE_OUTSIDE_CBMEM, then a
helper function to determine the caching region in SMM
should be implemented. Add the same to FSP2.0 driver.
FSP1.1 driver had the same implementation hence copied stage_cache.c.

The SoC code should implement the smm_subregion to provide
the base and size of the caching region within SMM. The fsp/memmap.h
provides the prototype and we will reuse the same from FPS 1.1.

Change-Id: I4412a710391dc0cee044b96403c50260c3534e6f
Signed-off-by: Rizwan Qureshi <rizwan.qureshi@intel.com>
Reviewed-on: https://review.coreboot.org/16312
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins)
3 files changed