misc: add a crc32c self test to mkfs and repair

misc: add a crc32c self test to mkfs and repair

Enhance mkfs and xfs_repair to run the crc32c self test when they start
up, and refuse to continue if the self test fails.   We don't want to
format a filesystem if the checksum algorithm produces incorrect
results, and we especially don't want repair to tear a filesystem apart
because it thinks the checksum is wrong.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>