ARM: ux500: move MMC/SD/SDIO pin control to the device tree

This moves the static, device-tied pin control configuration
out of the board file board-mop500-pins.c and into the device
tree. Add entries for SDI1 and SDI2 on the Snowball so that the
WLAN pins on SDI1 can be used further on, and the unused pins
on SDI2 can be put to sleep.

Cc: Lee Jones <lee.jones@linaro.org>
Cc: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>