libxfs: move header files

Move all the header files that are shared with userspace into
libxfs. This is done as one big chunk simpy to get it done quickly.
Signed-off-by: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
Signed-off-by: NDave Chinner <david@fromorbit.com>