cbfs: Pull handling of the CBFS_CACHE mem_pool into CBFS core

This patch pulls control of the memory pool serving allocations from the
CBFS_CACHE memlayout area into cbfs.c and makes it a core part of the
CBFS API. Previously, platforms would independently instantiate this as
part of boot_device_ro() (mostly through cbfs_spi.c). The new cbfs_cache
pool is exported as a global so these platforms can still use it to
directly back rdev_mmap() on their boot device, but the cbfs_cache can
now also use it to directly make allocations itself. This is used to
allow transparent decompression support in cbfs_map().

Signed-off-by: Julius Werner <jwerner@chromium.org>
Change-Id: I0d52b6a8f582a81a19fd0fd663bb89eab55a49d9
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49333
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/commonlib/Makefile.inc

@@ -5,6 +5,7 @@ verstage-y += mem_pool.c
 romstage-y += mem_pool.c
 ramstage-y += mem_pool.c
 postcar-y += mem_pool.c
+smm-y += mem_pool.c
 
 bootblock-y += iobuf.c
 verstage-y += iobuf.c