powerpc: Make macintosh/mediabay driver depend on CONFIG_BLOCK

Fixes this build error:

In file included from drivers/macintosh/mediabay.c:21:
include/linux/ide.h:605: error: field 'request_sense_rq' has incomplete type

Signed-off-by: Alexander Beregalov <a.beregalov@gmail.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>