io: block: fix unaligned buffer ...

If buffer address parameter isn't aligned, it may cause
DMA issue in block device driver, as eMMC. Now check the buffer
address. If it's not aligned, use temporary buffer in io block
driver instead.

Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>

IO: support block device type ...

FIP is accessed as memory-mapped type. eMMC is block device type.
In order to support FIP based on eMMC, add the new io_block layer.

io_block always access eMMC device as block size. And it'll only
copy the required data into buffer in io_block driver. So preparing
an temporary buffer is required.

When use io_block device, MAX_IO_BLOCK_DEVICES should be declared
in platform_def.h. It's used to support multiple block devices.

Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>