xfs: embedded the attrlist cursor into struct xfs_attr_list_context

The attrlist cursor only exists as part of an attr list context, so
embedd the structure instead of pointing to it.  Also give it a proper
xfs_ prefix and remove the obsolete typedef.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Chandan Rajendra <chandanrlinux@gmail.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>