Enable the scaling engine for upscaling a single plane using the polyphase
scaler. No image enhancement support or downscaling yet*, and composition
result scaling is not implemented.

* Downscaling a plane requires mclk > pxlclk.
Signed-off-by: Mihail Atanassov <mihail.atanassov@arm.com>
Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>