[ARM] 5035/1: Ensure that zone adjustment is done only on CM-X270

Adjust zones for PCI DMA only if machine_is_armcore() to allow running
the same kernel on different PXA machines.

Signed-off-by: Mike Rapoport <mike@compulab.co.il>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>