ARM: ux500: Enable support for UHS-I SD-cards

By setting the host capabilities MMC_CAP_UHS_SDR12|25 for
the SD card device we enable support for UHS cards. The
supported mode is SDR12 and SDR25.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>