x86: Add more common routines to manipulate mrc cache

x86: Add more common routines to manipulate mrc cache

This adds mrccache_reserve(), mrccache_get_region() and
mrccache_save() APIs to the mrccache codes. They are ported
from the ivybridge implementation, but with some changes.
For example, in the mrccache_reserve(), ivybridge version
only reserves the pure MRC data, which causes additional
malloc() when saving the cache as the save API needs some
meta data. Now we change it to save the whole MRC date plus
the meta data to elinimate the need for the malloc() later.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>