[ARM] Fix PCI_DMA_BUS_IS_PHYS for ARM

PCI_DMA_BUS_IS_PHYS was defined to be zero, which meant we ignored
the DMA mask for IDE and SCSI transfers.  This is wrong - we have
no DMA translation hardware.  We want to obey DMA masks so that the
block layer performs bouncing itself.

Reported-by: Mikael Pettersson <mikpe@it.uu.se>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>