futility/cmd_validate_rec_mrc: Update futility to use new MRC struct
futility/cmd_validate_rec_mrc: Update futility to use new MRC struct

1. Use mrc_metadata structure with new fields for header checksum and
data checksum.
2. Use region file metadata to ensure there is only one metadata block
present and only one slot in recovery MRC cache. Use the offset and size
based on values in metadata block.

BUG=chrome-os-partner:61306
BRANCH=None
TEST=Verified that recovery MRC cache is verified using futility.

Change-Id: I68b2d75ea70fdaef6c87cdaa6ce97656e8a8bddc
Signed-off-by: Furquan Shaikh <6be5c96c464778f89679b1062a2e0a6af93d2aa5@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/424213
Reviewed-by: Aaron Durbin <af0622ab041e8b0f8e5819838dcc93898196e71f@chromium.org>

coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot