pstore/zone: Introduce common layer to manage storage zones

Implement a common set of APIs needed to support pstore storage zones,
based on how ramoops is designed. This will be used by pstore/blk with
the intention of migrating pstore/ram in the future.

Signed-off-by: WeiXiong Liao <liaoweixiong@allwinnertech.com>
Link: https://lore.kernel.org/lkml/20200511233229.27745-2-keescook@chromium.org/


Co-developed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>