mmc: sdhci-pci: Avoid 3.3V signaling on some NI 904x

On some NI 904x devices, using 3.3V signaling for extended periods of
time will physically damage the pads connected to the SDHC, eventually
causing complete failure of the controller. To work around this,
require that we avoid 3.3V signaling.

Signed-off-by: Kyle Roeschley <kyle.roeschley@ni.com>
Signed-off-by: Jennifer Dahm <jennifer.dahm@ni.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>