sh: Migo-R MMC support using spi_gpio and mmc_spi.

This patch adds CN9 MMC support for MigoR using the mmc_spi
driver on top of the bitbanging spi_gpio driver.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>