mmc: sdhci-msm: Add support to store supported vdd-io voltages

During probe check whether the vdd-io regulator of sdhc platform device
can support 1.8V and 3V and store this information as a capability of
platform device.

Signed-off-by: Vijay Viswanath <vviswana@codeaurora.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>