package/webkitgtk: select missing multimedia deps

package/webkitgtk: select missing multimedia deps

Select a few missing multimedia related dependencies:

- BR2_PACKAGE_GST1_PLUGINS_GOOD_PLUGIN_AUTODETECT is needed for
  "autoaudiosink"; not having this element can cause a crash as
  it is used unconditionally.
- BR2_PACKAGE_GST1_PLUGINS_GOOD_PLUGIN_MATROSKA and
  BR2_PACKAGE_GST1_PLUGINS_GOOD_PLUGIN_VPX are needed for
  WebM video playback.

Note that BR2_PACKAGE_GST1_PLUGINS_GOOD_PLUGIN_VPX depends on THREADS
(because of libvpx), but webktigtk already depend on libgtk3, which
depends on THREADS. The probability that GTK3 drops the dependency on
THREADS is sufficiently close to zero that we need not account for that.
So we do not propagate the THREADS dependency for this option.

Signed-off-by: Adrian Perez de Castro <aperez@igalia.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>