Adds handling needed for the pre-encode downscaling for superres
encoding. Makes use of the existing resizing functionality, just
adjusting the target resolution after the resize logic and before the
resize has actually occurred.

Since the upscaling portion of superres is not yet implemented, superres
scaling is not yet allowed to trigger. The numerator is set to be equal
to the denominator and the superres_pending flag is not set.

Change-Id: Ia5dac752d653c3bda319f0c8196e95bac2c8c554