This patch forces the vertical filtering for the top and bottom
rows of a processing unit for the Wiener filter to be 5-tap.
The 5-taps are derived from the primary 7-tap fitler by forcing
the taps at the end to be zero, and absorbing their weights into
the other taps to maintain normalization.
This will effectively reduce the line buffer size for luma Wiener
filter to 4 (from 6).

Change-Id: I5e21b58369777eabf553a8987387d112f98a5598