sdhci: use PIO when DMA can't satisfy the request

Some controllers have been designed on the assumption that all transfers
will be 32-bit aligned, both in start address and in size. This is not a
guarantee the SDHCI specification provides and not one we can provide.

Revert back to PIO for individual requests in order to work around the
hardware bug.

Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>