[ARM] pxa/cm-x300: add support for PXA310 cpu

CM-X300 can be assembled with PXA300 and PXA310 CPU. Provide support for
both CPU variants.

Signed-off-by: Igor Grinberg <grinberg@compulab.co.il>
Signed-off-by: Mike Rapoport <mike@compulab.co.il>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>