NFM cpu: Import sunxi MMC driver from uboot

Change-Id: I8417875737a5f8e1dc21325ad5d6d245423f68cb
NFM cpu: Add clock reg definitions for SD clock

Change-Id: I88763072c8a541ddba794e79fb55e82eb2f187a9
cubieboard: add basic SD init and testing

Change-Id: I63302b87b583ed62794559238b8b1ae19aba3f81
NFM cpu: use SD card for bootblock media

Change-Id: Ie0b123023c53e485c41650c1fc7b0fb69a286a30