sunxi: video: Add simplefb support

Add simplefb support, note this depends on the kernel having support for
the clocks property which has recently been added to the simplefb devicetree
binding.

Signed-off-by: Luc Verhaegen <libv@skynet.be>
[hdegoede@redhat.com: Use pre-populated simplefb node under /chosen as
 disussed on the devicetree list]
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk&gt;.>