[ARM] pxa: select CPU_PXA310 for MACH_COLIBRI300

MACH_COLIBRI300 is supposed to support both PXA300 and PXA310, select
the missing CPU_PXA310.

Signed-off-by: Eric Miao <eric.y.miao@gmail.com>
Acked-by: Daniel Mack <daniel@caiaq.de>