ARM: realview: add MMCI to the PB1176 DTS

This adds the MMC/SD card reader (MMCI) block to the
RealView PB1176 DTS file. Add a special MCLK derived clock
and a fixed regulator to represent the 3.3V rail hardwired
to the MMC reader on the board.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>