xilinxfb: xilinx framebuffer device driver

Add support for the video controller IP block included into Xilinx ML300 and
ML403 reference designs.

Signed-off-by: Andrei Konovalov <akonovalov@ru.mvista.com>
Signed-off-by: Antonino Daplas <adaplas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>