Add support overlays of non-framebuffer format

Implement flexible support of overlay format that do not match
the framebuffer format. This allows the use of a 32bpp overlay
in 16bpp mode in sunxifbsink, for example.
Make overlay support more flexible, and support YUV in sunxifbsink

The overlay format support is now more flexible with an array of
GStreamer video format supplied by the driver.

sunxibsink now supports hardware overlays for a full set of YUV
formats.

Add max used video memory property, and only map the amount of
video memory that is used.

Add missing file sunxi_disp_ioctl.h to allow compilation of
sunxifbsink.