configure: Virtfs doesn't require libcap.

Only proxy helper does.
Reviewed-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NKusanagi Kouichi <slash@ac.auone-net.jp>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

configure

@@ -2889,9 +2889,11 @@ tools=
 if test "$softmmu" = yes ; then
   tools="qemu-img\$(EXESUF) qemu-io\$(EXESUF) $tools"
   if test "$virtfs" != no ; then
-      if test "$cap" = yes && test "$linux" = yes && test "$attr" = yes ; then
+      if test "$linux" = yes && test "$attr" = yes ; then
 	  virtfs=yes
+	  if test "$cap" = yes ; then
 	      tools="$tools fsdev/virtfs-proxy-helper\$(EXESUF)"
+	  fi
       else
 	  if test "$virtfs" = yes; then
 	      feature_not_found "virtfs"