mmc: mmci: add ddrmode mask to variant data

This patch adds ddrmode mask to variant structure giving more flexibility
to the driver to support more SOCs which have different datactrl register
layout.

Without this patch datactrl register is updated with incorrect ddrmode mask,
resulting in failures on Qualcomm SD Card Controller.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
[Ulf Hansson] Resolved conflict
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>