[AFS/AF_RXRPC]: Miscellaneous fixes.

Make miscellaneous fixes to AFS and AF_RXRPC:

 (*) Make AF_RXRPC select KEYS rather than RXKAD or AFS_FS in Kconfig.

 (*) Don't use FS_BINARY_MOUNTDATA.

 (*) Remove a done 'TODO' item in a comemnt on afs_get_sb().

 (*) Don't pass a void * as the page pointer argument of kmap_atomic() as this
     breaks on m68k.  Patch from Geert Uytterhoeven <geert@linux-m68k.org>.

 (*) Use match_*() functions rather than doing my own parsing.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>