libvpx

Move frame re-sizing into the recode loop

The point at which frames are scaled to their
coded dimensions is moved into the re-code loop.

This is in preparation for a further patch that
will add logic into the re-code loop to reduce
the coded frame size if the encoder is struggling
to hit the target data rate at the native frame
size.

Change-Id: Ie4131f5ec6fb93148879f6ce96123296442bf2d1