drivers/mmc: make mmc_ext_csd aligned with 16 char
drivers/mmc: make mmc_ext_csd aligned with 16 char

DMA is always used in mmc driver. So the buffer address should
always follow the DMA limitation.

There're same requirement in mmc_read_blocks()/mmc_write_blocks()
on parameter buf. Since parameter buf comes from io_block driver,
it's already handled in io_block driver.

At here, just make the minimum address alignment on 16 chars.

Signed-off-by: Haojian Zhuang <979139d45d262f0480136b0da512e0afa0fe79d3@linaro.org>

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware