i420->yuv2 converter: disabled altivec usage if video's width isn't a multiple of 32
i420->yuv2 converter: disabled altivec usage if video's width isn't a multiple of 32

This fixes the video output on PowerPC based Macs. A proper fix would be welcome.

Forward-port of [c036a9961b04ef03e8ae6951c78f1e550e57395a]

jomanmuk/vlc-2.2,krichter722/vlc,vlc-mirror/vlc,vlc-mirror/vlc,vlc-mirror/vlc,krichter722/vlc,xkfz007/vlc,jomanmuk/vlc-2.2,jomanmuk/vlc-2.1,vlc-mirror/vlc,krichter722/vlc,krichter722/vlc,jomanmuk/vlc-2.2,jomanmuk/vlc-2.1,krichter722/vlc,vlc-mirror/vlc,jomanmuk/vlc-2.1,shyamalschandra/vlc,xkfz007/vlc,shyamalschandra/vlc,krichter722/vlc,vlc-mirror/vlc-2.1,xkfz007/vlc,shyamalschandra/vlc,xkfz007/vlc,jomanmuk/vlc-2.1,vlc-mirror/vlc-2.1,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.1,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.2,vlc-mirror/vlc-2.1,shyamalschandra/vlc,xkfz007/vlc,shyamalschandra/vlc,jomanmuk/vlc-2.2,shyamalschandra/vlc,krichter722/vlc,vlc-mirror/vlc,jomanmuk/vlc-2.2,jomanmuk/vlc-2.1,jomanmuk/vlc-2.1,xkfz007/vlc,jomanmuk/vlc-2.2,shyamalschandra/vlc,xkfz007/vlc,vlc-mirror/vlc,vlc-mirror/vlc-2.1,vlc-mirror/vlc-2.1