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 wrong ddrmode mask on non
ST SOCs, resulting in card detection failures.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>