package/qt: webkit needs gst-plugins-base

package/qt: webkit needs gst-plugins-base

QtWebkit needs gstreamer-0.10 and the 'app' plugins, so we depend on
gstreamer and select the required plugins.

We can't select gstreamer as that would cause circular dependencies in
kconfig:

    package/kodi/Config.in:37:error: recursive dependency detected!
    package/kodi/Config.in:37:      symbol BR2_PACKAGE_KODI depends on BR2_PACKAGE_KODI_EGL_GLES
    package/kodi/Config.in:16:      symbol BR2_PACKAGE_KODI_EGL_GLES depends on BR2_PACKAGE_HAS_LIBEGL
    package/opengl/libegl/Config.in:1:      symbol BR2_PACKAGE_HAS_LIBEGL is selected by BR2_PACKAGE_MESA3D_OPENGL_EGL
    package/mesa3d/Config.in:150:   symbol BR2_PACKAGE_MESA3D_OPENGL_EGL is selected by BR2_PACKAGE_MESA3D_GALLIUM_DRIVER_VIRGL
    package/mesa3d/Config.in:92:    symbol BR2_PACKAGE_MESA3D_GALLIUM_DRIVER_VIRGL depends on BR2_PACKAGE_MESA3D
    package/mesa3d/Config.in:1:     symbol BR2_PACKAGE_MESA3D is selected by BR2_PACKAGE_XDRIVER_XF86_VIDEO_IMX_VIV
    package/x11r7/xdriver_xf86-video-imx-viv/Config.in:1:   symbol BR2_PACKAGE_XDRIVER_XF86_VIDEO_IMX_VIV depends on BR2_PACKAGE_IMX_GPU_VIV_OUTPUT_X11
    package/freescale-imx/imx-gpu-viv/Config.in:34: symbol BR2_PACKAGE_IMX_GPU_VIV_OUTPUT_X11 is part of choice <choice>
    package/freescale-imx/imx-gpu-viv/Config.in:27: choice <choice> contains symbol <choice>
    package/freescale-imx/imx-gpu-viv/Config.in:27: choice <choice> contains symbol BR2_PACKAGE_FREESCALE_IMX
    package/freescale-imx/Config.in:1:      symbol BR2_PACKAGE_FREESCALE_IMX is selected by BR2_PACKAGE_GST_FSL_PLUGINS
    package/gstreamer/gst-fsl-plugins/Config.in:8:  symbol BR2_PACKAGE_GST_FSL_PLUGINS depends on BR2_PACKAGE_GSTREAMER
    package/gstreamer/gstreamer/Config.in:5:        symbol BR2_PACKAGE_GSTREAMER is selected by BR2_PACKAGE_QT_WEBKIT
    package/qt/Config.in:464:       symbol BR2_PACKAGE_QT_WEBKIT depends on BR2_PACKAGE_QT
    package/qt/Config.in:5: symbol BR2_PACKAGE_QT is selected by BR2_PACKAGE_PYTHON_PYQT
    package/python-pyqt/Config.in:5:        symbol BR2_PACKAGE_PYTHON_PYQT depends on BR2_PACKAGE_PYTHON
    package/python/Config.in:5:     symbol BR2_PACKAGE_PYTHON is selected by BR2_PACKAGE_KODI

This one is fairly complicated to fix properly, so it is easier to just
depend on gstreamer.

Also rework the comment when QtWebkit is not available.

Fixes:
    http://autobuild.buildroot.org/results/84d/84d338b70c8ce3f21dd202de387326f18526aa63/
    http://autobuild.buildroot.org/results/379/379ad4eadf5af7e1d5b977bc229d3fcaba25b4fe/
    [...]

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>