ARM: ux500: Enable 100MHz for SD/SDIO/MMC devices

We are able to cope with an SDMMC clock of 100MHz so let's
make use of the full frequency instead of the half.

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