configure: add (empty) avr32 arch case

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@17479 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

configure

@@ -1374,6 +1374,8 @@ case "$arch" in
     arm|armv[4567]*l)
         arch="arm"
     ;;
+    avr32)
+    ;;
     bfin)
         arch="bfin"
     ;;