OMAP: Add support for VRFB rotation engine

VRFB rotation engine is a block in OMAP2/3 that offers 12 independent
contexts that can be used for framebuffer rotation.

Each context has a backend area of real memory, where it stores the
pixels in undisclosed format. This memory is offered to users via 4
virtual memory areas, which see the same memory area in different
rotation angles (0, 90, 180 and 270 degrees).

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>