src/lib: Add Kconfig option for SPD cache in FMAP

Currently, the option to cache dimm SPD data in an FMAP region
is closely coupled to a single board (google/hatch) and requires
a custom FMAP to utilize.

Loosen this coupling by introducing a Kconfig option which adds
a correctly sized and aligned RW_SPD_CACHE region to the default FMAP.
Add a Kconfig option for the region name, replacing the existing hard-
coded instance in spd_cache.h. Change the inclusion of spd_cache.c to
use this new Kconfig, rather than the board-specific one currently used.
Lastly, have google/hatch select the new Kconfig when appropriate to
ensure no change in current functionality.

Test: build/boot WYVERN google/hatch variant with default FMAP, verify
FMAP contains RW_SPD_CACHE, verify SPD cache used via cbmem log.

Also tested on an out-of-tree Purism board.

Change-Id: Iee0e7acb01e238d7ed354e3dbab1207903e3a4fc
Signed-off-by: Matt DeVillier <matt.devillier@puri.sm>
---
M Makefile.inc
M src/include/spd_cache.h
M src/lib/Kconfig
M src/lib/Makefile.inc
M src/mainboard/google/hatch/Kconfig
M util/cbfstool/default-x86.fmd
6 files changed, 32 insertions(+), 2 deletions(-)