Currently the mmc_change_freq and mmc_startup functions allocates
buffers on the stack that are passed down to the MMC device driver.
These buffers could be unaligned to the L1 dcache line size.  This
causes problems when using DMA and with caches enabled.

This patch correctly cache alignes the buffers used for reading the
ext_csd data from an MMC device.

Signed-off-by: Anton Staaf <robotboy@chromium.org>
Cc: Lukasz Majewski <l.majewski@samsung.com>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Albert ARIBAUD <albert.u.boot@aribaud.net>