sunxi: Remove mmc DMA support

sunxi: Remove mmc DMA support

The DMA code in sunxi_mmc.c is broken. mmc_trans_data_by_dma() allocates the
dma descriptors on the stack, and then exits while the dma transfer is in
progress, so the dma engine is reading stack memory which at that point may
be re-used. So far we've gotten away with this by luck, but recent u-boot
changes have shifted the stack start address by 16 bytes, which combined
with dma alignment now exposes this problem.

Since we end up just busy waiting for the dma engine anyway, this commit
fixes things by simply removing the dma code, resulting in smaller bug-free
code.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>