drivers/video: fsl-diu-fb: add hardware cursor support

The Freescale DIU supports a 32x32 color hardware cursor.  Framebuffer
cursors are monochrome, so the driver converts the image data to the
format that the DIU expects and then programs to hardware accordingly.

The support cursor enabling/disabling, we provide two cursor image buffers.
One is always blank (all zeroes), and the other contains the real cursor
image data.  To disable the cursor (used typically for cursor blinking),
we just tell the hardware to use the blank cursor data.

Signed-off-by: Timur Tabi <timur@tabi.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>