[MIPS] No ide_default_io_base() if PCI IDE was not found

Revert b5438582

 and add
no_pci_devices() check to avoid crash due to early calling of
pci_get_class().

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>