Add missing --disable-armv6t2 to help output.

Originally committed as revision 16542 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -146,6 +146,7 @@ show_help(){
   echo "  --disable-armv5te        disable armv5te optimizations"
   echo "  --disable-armv6          disable armv6 optimizations"
   echo "  --disable-armvfp         disable ARM VFP optimizations"
+  echo "  --disable-armv6t2        disable armv6t2 optimizations"
   echo "  --disable-iwmmxt         disable iwmmxt optimizations"
   echo "  --disable-mmi            disable MMI optimizations"
   echo "  --disable-neon           disable neon optimizations"