Small abstraction so that kernel pointer is passed in to filter 1st/2nd pass.
Small abstraction so that kernel pointer is passed in to filter 1st/2nd pass.

This should make it easier to add the bilinear filter, since all of the
arguments/return types and so forth match subpixel prediction.

awatry/libvpx.opencl,awatry/libvpx.opencl,awatry/libvpx.opencl,awatry/libvpx.opencl