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

1. add common GPIO handling code into [arch/arm/plat-pxa]

2. common code in <mach/gpio.h> moved into <plat/gpio.h>, new processors
   should implement its own <mach/gpio.h>, provide the following required
   definitions and '#include <plat/gpio.h>' in the end:

   - GPIO_REGS_VIRT for mapped virtual address of the GPIO registers'
     physical I/O memory

   - macros of GPLR(), GPSR(), GPDR() for constant optimization for
     functions gpio_{set,get}_value() (so that bit-bang code can still
     have tolerable performance)

   - NR_BUILTIN_GPIO for the number of onchip GPIO

   - definitions of __gpio_is_inverted() and __gpio_is_occupied(), they
     can be either macros or inlined functions
Signed-off-by: NEric Miao <eric.miao@marvell.com>

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: NEric Miao <eric.miao@marvell.com>