xfs: refactor all the EFI/EFD log item sizeof logic

xfs: refactor all the EFI/EFD log item sizeof logic

Refactor all the open-coded sizeof logic for EFI/EFD log item and log
format structures into common helper functions whose names reflect the
struct names.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>