This commit enables SSE2 implementation of 8x8 inverse ADST/DCT
transform. The runtime goes from 1216 cycles -> 266 cycles.
For bus_cif at 2000 kbps, the overall runtime reduces from
253707ms -> 248430ms, i.e., 2% speed-up at speed 0.

Change-Id: Ib0372e17e9162d7b11a10d653b1c8be547c878fb