[MMC] sdhci: force DMA on some controllers

Some controllers incorrectly report that the cannot do DMA.  Forcefully enable
it for those that we know it works fine on.

Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>