Replace --disable-libv4l2 with --disable-v4l2

This disables V4L2 completely.
(cherry picked from commit fd8502cee82371a65b2eeeb230fbe63917bd84ff)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

configure.ac

@@ -1869,21 +1869,21 @@ fi
 dnl
 dnl  Video4Linux 2
 dnl
-AC_ARG_ENABLE(libv4l2, [AS_HELP_STRING([--disable-libv4l2],
-  [disable userspace V4L2 library (default auto)])])
+AC_ARG_ENABLE(v4l2, [AS_HELP_STRING([--disable-v4l2],
+  [disable Video4Linux version 2 (default auto)])])
 AC_ARG_ENABLE(pvr, [AS_HELP_STRING([--enable-pvr],
   [support PVR V4L2 cards (default disabled)])])
 have_v4l2="no"
-AC_CHECK_HEADERS([linux/videodev2.h sys/videoio.h], [
-  have_v4l2="yes"
+AS_IF([test "$enable_v4l2" != "no"], [
+  AC_CHECK_HEADERS([linux/videodev2.h sys/videoio.h], [
+    have_v4l2="yes"
+  ])
 ])
 AS_IF([test "$have_v4l2" = "yes"], [
-  AS_IF([test "${enable_libv4l2}" != "no"], [
-    PKG_CHECK_MODULES(LIBV4L2, libv4l2, [
-      AC_DEFINE(HAVE_LIBV4L2, 1, [Define to 1 if libv4l2 is available])
-    ], [
-      AC_MSG_WARN([${LIBV4L2_PKG_ERRORS}.])
-    ])
+  PKG_CHECK_MODULES(LIBV4L2, libv4l2, [
+    AC_DEFINE(HAVE_LIBV4L2, 1, [Define to 1 if libv4l2 is available])
+  ], [
+    AC_MSG_WARN([${LIBV4L2_PKG_ERRORS}.])
   ])
   AS_IF([test "${enable_pvr}" = "yes"], [
     VLC_ADD_PLUGIN([pvr])