dec_neon: add LD4 intra predictor
dec_neon: add LD4 intra predictor

based on SSE2 version, ~55% faster

Change-Id: I782282ffc31dcf238890b3ba0decccf1d793dad0

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