PATA: RPC now selects HAVE_PATA_PLATFORM for pata platform driver

The RPC machine type now selects HAVE_PATA_PLATFORM so we can remove
the special case in the PATA_PLATFORM configuration code.

Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>