[ARM] pxa: move pxa2xx chip selects definitions out of pxa-regs.h

The definitions of PXA_CS<x>_PHYS are really PXA2xx specific and should
be moved out of pxa-regs.h. As an illustration, the PXA3xx static chip
selects definitions are added into pxa3xx-regs.h.

Signed-off-by: Eric Miao <eric.miao@marvell.com>