xfs: mark inodes dirty before issuing I/O

To make sure they get properly waited on in sync when I/O is in flight and
we latter need to update the inode size.  Requires a new helper to check if an
ioend structure is beyond the current EOF.

Signed-off-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>
Signed-off-by: Alex Elder <aelder@sgi.com>