We have three rotation methods supported by the SoCs with DSS: DMA,
VRFB and TILER.

DMA rotation works in theory on all DSS platforms, but in practice it's
unusable due to the huge amount of memory bandwidth it uses, and has
never really been used.

VRFB is available on OMAP3, but is not supported by omapdrm, even though
we have some code for it in the dispc driver.

TILER is supported on OMAP4/OMAP5/DRA7/AM5 platforms, but has some
driver bugs.

To clean up the driver to help fixing the TILER issues, this patch drops
the DMA and VRFB rotation support, leaving only TILER rotation.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>