configure: Use pkg-config for libdc1394 discovery

Since not all systems need the libraw1394 dependency, let pkg-config
provide the list of libraries actually needed.

The libdc1394-2.pc file has been included since version 2 (2008-01-05),
so it should be safe to use.

configure

@@ -4248,7 +4248,7 @@ fi
 
 # libdc1394 check
 if enabled libdc1394; then
-    { check_lib dc1394/dc1394.h dc1394_new -ldc1394 -lraw1394 &&
+    { require_pkg_config libdc1394-2 dc1394/dc1394.h dc1394_new &&
         enable libdc1394_2; } ||
     { check_lib libdc1394/dc1394_control.h dc1394_create_handle -ldc1394_control -lraw1394 &&
         enable libdc1394_1; } ||