pxa3xx_nand: move pxa3xx_nand.h common into plat directory

Since the same nand controller is shared between ARCH_PXA and ARCH_MMP. Move
the pxa3xx_nand.h from mach directory to plat directoy.

Signed-off-by: Haojian Zhuang <haojian.zhuang@marvell.com>
Cc: David Woodhouse <david.woodhouse@intel.com>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>