mmc: moxart: Add MOXA ART SD/MMC driver

Add SD/MMC driver for MOXA ART SoCs.

The "MOXA ART MMC controller" is likely a faraday "ftsdc010",
a controller with support in U-Boot:

http://git.denx.de/?p=u-boot.git;a=blob;f=drivers/mmc/ftsdc010_mci.c



Signed-off-by: Jonas Jensen <jonas.jensen@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Chris Ball <chris@printf.net>