sunxi-mmc: Add new sunxi-mmc driver from a20 code dump

The sunxi-3.3-cubieboard2 branch has a new mmc driver, which is much cleaner,
properly using the existing mmc framework for many things, and offers more
features then the original driver we carry in sunxi-3.4.

Note this commit just adds the driver as is. The next commits will actually
hook it up to the build system and port it to sunxi-3.4 in sofar that is
needed.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
sunxi-mmc: hookup new sunxi-mci driver in buildsys and make it build (and work)

For sun7i for now, also using this for sun5i should be easy, making it work
for sun4i will require slightly more work.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Merge remote-tracking branch 'jwrdegoede/sunxi-3.4-a20-wip' into sunxi-3.4-a20