xfs_{db,repair}: use accessor functions for summary info words

xfs_{db,repair}: use accessor functions for summary info words

Port xfs_db and xfs_repair to use get and set functions for rtsummary
words so that we can redefine the ondisk format with a specific
endianness.  Note that this requires the definition of a distinct type
for ondisk summary info words so that the compiler can perform proper
typechecking.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bill O'Donnell <bodonnel@redhat.com>