LIBATA: Add HAVE_PATA_PLATFORM to select PATA_PLATFORM driver

Add HAVE_PATA_PLATFORM to select the pata platform driver
to ensure that we do not end up with a long 'depends on' list
when other users of this driver turn up.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>