libata: Allow pata_legacy to be built on non-ISA but PCI systems

This is needed for some unsupported hardware setups on strange 64bit
mainboards where crazy stuff has been done like putting flash ata adapters
on the LPC bus, or where the real hardware is hidden/confused.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>