linux-user: Check for Linux USBFS in configure

In preparation for adding user mode emulation support for the
Linux usbfs interface, check for its kernel header.
Signed-off-by: NCortland Tölva <cst@tolva.net>
Reviewed-by: NLaurent Vivier <laurent@vivier.eu>
Message-Id: <20181008163521.17341-2-cst@tolva.net>
Signed-off-by: NLaurent Vivier <laurent@vivier.eu>

configure

@@ -4202,7 +4202,14 @@ if compile_prog "" "" ; then
   memfd=yes
 fi
 
-
+# check for usbfs
+have_usbfs=no
+if test "$linux_user" = "yes"; then
+  if check_include linux/usbdevice_fs.h; then
+    have_usbfs=yes
+  fi
+  have_usbfs=yes
+fi
 
 # check for fallocate
 fallocate=no
@@ -6310,6 +6317,9 @@ fi
 if test "$memfd" = "yes" ; then
   echo "CONFIG_MEMFD=y" >> $config_host_mak
 fi
+if test "$have_usbfs" = "yes" ; then
+  echo "CONFIG_USBFS=y" >> $config_host_mak
+fi
 if test "$fallocate" = "yes" ; then
   echo "CONFIG_FALLOCATE=y" >> $config_host_mak
 fi