mmc: Add OpenFirmware bindings for SDHCI driver

This patch adds a new driver: sdhci-of. The driver is similar to
the sdhci-pci, it contains common probe code, and controller-specific
ops and quirks.

So far there are only Freescale eSDHC ops and quirks.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>