libext2fs: optimize the CRC32c implementation

libext2fs: optimize the CRC32c implementation

The crc32c implementation in the kernel has been refactored a bit to
reduce the amount of code that needs to be maintained, and to speed up
tune2fs/e2fsck on PowerPC by 5-10%.  Port the crc32c changes over, and
provide a crc32_be so that we can remove the duplicate functionality
from e2fsck.  Also drop crc32c_be and crc32_le since neither got used.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>