Add ram_block_store component

The ram_block_store is a block_store implementation intended for use
in test integrations. Rather than use real NV storage, it uses an
area of normal memory for storing blocks. Test cases added that
exercise the ram_block_store using the base block_store interface.

Signed-off-by: Julian Hall <julian.hall@arm.com>
Change-Id: If9c2ad287fddedf6a5b7f8c9a5c70a7111978b3a
9 files changed