frv: unexport kmap_atomic_to_page

This patch removes the no longer used export of kmap_atomic_to_page.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>