mmc: don't use DMA on newer ENE controllers

Even the newer ENE controllers have bugs in their DMA engine that make
it too dangerous to use. Disable it until someone has figured out under
which conditions it corrupts data.

This has caused problems at least once, and can be found as bug report
10925 in the kernel bugzilla.

Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>