The scaling filter with zero shift will give sub-sampling for
2x downsampling. Allow for a phase shift to get an averaging filter.

Usage is for source scaling in 1 pass SVC mode for 1:2 downscale.
Reduces aliasing in downsampled image.

Keep the phase to 0/off for now.

Change-Id: Ic547ea0748d151b675f877527e656407fcf4d51e