agp: uninorth: make two functions static

Both ‘uninorth_remove_memory’ and ‘null_cache_flush’ can be made
static. So make them.

Silence the following gcc warning (W=1):

  drivers/char/agp/uninorth-agp.c:198:5: warning: no previous prototype for ‘uninorth_remove_memory’ [-Wmissing-prototypes]

and

  drivers/char/agp/uninorth-agp.c:473:6: warning: no previous prototype for ‘null_cache_flush’ [-Wmissing-prototypes]

Signed-off-by: Mathieu Malaterre <malat@debian.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>