MIPS: dspr2: added optimization for simple filtering functions
MIPS: dspr2: added optimization for simple filtering functions

affected functions: SimpleVFilter16, SimpleHFilter16,
                    SimpleVFilter16i and SimpleHFilter16i

noticed bug in FilterLoop26 (fix included in this patch)

Change-Id: I72d9c1e45cbac6393eba52bb549b04924d463e30

redengineer/libwebp,imazen/libwebp,zofuthan/libwebp,PKRoma/libwebp,matanbs/webm.libwebp,kalli123/webm.libwebp,altogother/webm.libwebp,jiehu5114/libwebp,ttyangf/libwebp,ya7lelkom/libwebp,gshORTON/webm.libwebp,Maria1099/webm.libwebp,jacklicn/libwebp,Aexyn/libwebp,jiehu5114/libwebp,gshORTON/webm.libwebp,gshORTON/webm.libwebp,ericmckean/webm.libwebp,Aexyn/libwebp,reimaginemedia/webm.libwebp,imazen/libwebp,ttyangf/libwebp,kalli123/webm.libwebp,altogother/webm.libwebp,Acidburn0zzz/webm.libwebp,redengineer/libwebp,jacklicn/libwebp,kleopatra999/webm.libwebp,abwiz0086/webm.libwebp,Acidburn0zzz/webm.libwebp,Maria1099/webm.libwebp,redengineer/libwebp,rxl194/libwebp,matanbs/webm.libwebp,Suvarna1488/webm.libwebp,yohunl/libwebp,Aexyn/libwebp,abwiz0086/webm.libwebp,altogother/webm.libwebp,kim42083/webm.libwebp,ericmckean/webm.libwebp,rxl194/libwebp,redengineer/libwebp,kalli123/webm.libwebp,ya7lelkom/libwebp,matanbs/webm.libwebp,kleopatra999/webm.libwebp,imazen/libwebp,kim42083/webm.libwebp,redengineer/libwebp,yohunl/libwebp,kim42083/webm.libwebp,yohunl/libwebp,rxl194/libwebp,Suvarna1488/webm.libwebp,iniwf/webm.libwebp,imazen/libwebp,Aexyn/libwebp,iniwf/webm.libwebp,Maria1099/webm.libwebp,jiehu5114/libwebp,ya7lelkom/libwebp,iniwf/webm.libwebp,rxl194/libwebp,zofuthan/libwebp,ericmckean/webm.libwebp,kleopatra999/webm.libwebp,altogother/webm.libwebp,reimaginemedia/webm.libwebp,reimaginemedia/webm.libwebp,Suvarna1488/webm.libwebp,iniwf/webm.libwebp,yohunl/libwebp,Maria1099/webm.libwebp,yohunl/libwebp,gshORTON/webm.libwebp,zofuthan/libwebp,abwiz0086/webm.libwebp,kim42083/webm.libwebp,Acidburn0zzz/webm.libwebp,ttyangf/libwebp,PKRoma/libwebp,kleopatra999/webm.libwebp,PKRoma/libwebp,ya7lelkom/libwebp,rxl194/libwebp,zofuthan/libwebp,reimaginemedia/webm.libwebp,webmproject/libwebp,Maria1099/webm.libwebp,reimaginemedia/webm.libwebp,PKRoma/libwebp,Suvarna1488/webm.libwebp,ttyangf/libwebp,matanbs/webm.libwebp,webmproject/libwebp,jacklicn/libwebp,kalli123/webm.libwebp,gshORTON/webm.libwebp,PKRoma/libwebp,iniwf/webm.libwebp,jiehu5114/libwebp,abwiz0086/webm.libwebp,ttyangf/libwebp,Suvarna1488/webm.libwebp,imazen/libwebp,altogother/webm.libwebp,jacklicn/libwebp,kleopatra999/webm.libwebp,zofuthan/libwebp,ya7lelkom/libwebp,ericmckean/webm.libwebp,Acidburn0zzz/webm.libwebp,matanbs/webm.libwebp,Acidburn0zzz/webm.libwebp,jiehu5114/libwebp,PKRoma/libwebp,webmproject/libwebp,Aexyn/libwebp,jacklicn/libwebp,ericmckean/webm.libwebp,webmproject/libwebp,kim42083/webm.libwebp,kalli123/webm.libwebp,abwiz0086/webm.libwebp,webmproject/libwebp