ext4: cache-align buffers so the invalidation works

ext4: cache-align buffers so the invalidation works

DMA buffer cache invalidation requires that buffers have cache-aligned
buffer locations and sizes. Use memalign() and ALLOC_CACHE_ALIGN_BUFFER()
to ensure this.

On Tegra at least, without this fix, the following fail commands fail in
u-boot-master/ext4, but succeeded at the branch's branch point in
u-boot/master. With this fix, the commands work again:

ext2ls mmc 0:1 /
ext2load mmc 0:1 /boot/zImage

Cc: Uma Shankar <uma.shankar@samsung.com>
Cc: Manjunatha C Achar <a.manjunatha@samsung.com>
Cc: Iqbal Shareef <iqbal.ams@samsung.com>
Cc: Hakgoo Lee <goodguy.lee@samsung.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Tom Rini <trini@ti.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>