qt5webkit: add WEBKIT_CONFIG+=use_glib on libsoup enabled builds

use_glib is set in gstreamer builds but not in libsoup only builds whereas there exist a dependency on glibc
rpi_webkitgtk_defconfig should enable webkitgtk-shell.
Enable HTML5 Video support in WebKitGTK+.
Add the patch that contains the necessary changes for zero-copy, efficient video rendering.
Bump the webkitgtk-shell commit tag.
Merge pull request #46 from zdobersek/webkitgtk

WebKitGTK+ update