mmc: sdhci: Set DMA mask when adding host

Set the DMA mask in sdhci_add_host() after we determined the
capabilities of the device. 64-bit devices in particular are given the
proper mask that ensures bounce buffers are not used.

Also disable DMA if no proper DMA mask can be set, as the DMA-API
documentation specifies.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>