mmc: sdhci: Intel Medfield support

Basic support for the Intel Medfield devices

Give them their own quirks as we will need to update this later.

Signed-off-by: Xiaochen Shen <xiaochen.shen@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Chris Ball <cjb@laptop.org>