1. introduce folder of 'arch/arm/plat-pxa' for common code across different
PXA processor families
2. initially moved DMA code into plat-pxa
3. common code in <mach/dma.h> moved into <plat/dma.h>, new processors
should implement its own <mach/dma.h>, provide the following required
definitions and '#include <plat/dma.h>' in the end:
- DMAC_REGS_VIRT for mapped virtual address of the DMA registers'
physical I/O memory
Signed-off-by: Eric Miao <eric.miao@marvell.com>
