On each MB, loopfiltering is done right after MB decoding. This
combines two loops in multi-threaded code into one, which reduces
number of synchronizations to half.
The above-row/left-col data are saved in temp buffers for
next-row/next MB decoding.
Tests on 4-core gLucid machine showed 10% decoder performance
gain with threads=4 (tulip clip). Testing on other platforms
isn't done yet.
Change-Id: Id18ea7c1e84965dabea65d4c01ca5bc056ddeac9
