ARM: enable fast_unaligned when --cpu=armv[67] is specified

Originally committed as revision 19308 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -1882,6 +1882,10 @@ if test $cpu != "generic"; then
             add_cflags -mcpu=$cpu
             enable fast_unaligned
         ;;
+        armv[67]*)
+            add_cflags -march=$cpu
+            enable fast_unaligned
+        ;;
         armv*)
             add_cflags -march=$cpu
         ;;