mmc: mmci: Add Qcom datactrl register variant

Instance of this IP on Qualcomm's SOCs has bit different layout for datactrl
register. Bit position datactrl[16:4] hold the true block size instead of power
of 2.

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