Add shift stage for PSNRHVS computation
Add shift stage for PSNRHVS computation

Ported from libvpx/nextgenv2: 195bf52

Change-Id: I85673c8299958b42cfde72821873cbc815a6f928

mbebenita/aom,smarter/aom,luctrudeau/aom,GrokImageCompression/aom,luctrudeau/aom,shacklettbp/aom,GrokImageCompression/aom,mbebenita/aom,shacklettbp/aom,shacklettbp/aom,luctrudeau/aom,mbebenita/aom,GrokImageCompression/aom,GrokImageCompression/aom,smarter/aom,mbebenita/aom,luctrudeau/aom,mbebenita/aom,GrokImageCompression/aom,luctrudeau/aom,shacklettbp/aom,smarter/aom,mbebenita/aom,smarter/aom,smarter/aom,GrokImageCompression/aom,mbebenita/aom,mbebenita/aom,luctrudeau/aom,mbebenita/aom,shacklettbp/aom,smarter/aom,shacklettbp/aom