configure: enable vsx together with altivec for ppc64el

The altivec optimizations on little endian ppc64 don't work without vsx.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

configure

@@ -4432,7 +4432,7 @@ unsigned int endian = 'B' << 24 | 'I' << 16 | 'G' << 8 | 'E';
 EOF
 od -t x1 $TMPO | grep -q '42 *49 *47 *45' && enable bigendian
 
-if  [ "$cpu" = "power7" ] || [ "$cpu" = "power8" ] ;then
+if  [ "$cpu" = "power7" ] || [ "$cpu" = "power8" ] || enabled ppc64; then
     if ! enabled bigendian && enabled altivec ;then
         enable vsx
     fi