xfs: include header files for prototypes

Fix this sparse warnings:
  fs/xfs/linux-2.6/xfs_ioctl.c:72:1: warning: symbol 'xfs_find_handle' was not declared. Should it be static?
  fs/xfs/linux-2.6/xfs_ioctl.c:249:1: warning: symbol 'xfs_open_by_handle' was not declared. Should it be static?
  fs/xfs/linux-2.6/xfs_ioctl.c:361:1: warning: symbol 'xfs_readlink_by_handle' was not declared. Should it be static?
  fs/xfs/linux-2.6/xfs_ioctl.c:496:1: warning: symbol 'xfs_attrmulti_attr_get' was not declared. Should it be static?
  fs/xfs/linux-2.6/xfs_ioctl.c:525:1: warning: symbol 'xfs_attrmulti_attr_set' was not declared. Should it be static?
  fs/xfs/linux-2.6/xfs_ioctl.c:555:1: warning: symbol 'xfs_attrmulti_attr_remove' was not declared. Should it be static?
  fs/xfs/linux-2.6/xfs_ioctl.c:657:1: warning: symbol 'xfs_ioc_space' was not declared. Should it be static?
  fs/xfs/linux-2.6/xfs_ioctl.c:1340:1: warning: symbol 'xfs_file_ioctl' was not declared. Should it be static?
  fs/xfs/support/debug.c:65:1: warning: symbol 'xfs_fs_vcmn_err' was not declared. Should it be static?
  fs/xfs/support/debug.c:112:1: warning: symbol 'xfs_hex_dump' was not declared. Should it be static?

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Felix Blyakher <felixb@sgi.com>