gst1-plugins-bad: add support for opengl

Commit 83e29f26 "gst1-plugins-bad: bump
version" (from 1.2.4 to 1.4.1) removed the configuration option for the
eglglessink plugin as a consequence of its removal in 1.3.1. However,
that commit did not add support for glimagesink, the plugin element to
be used as a replacement, which broke support for the EGL/GLES video
sink feature in Buildroot.

This new commit adds support for the OpenGL library and the
corresponding gl plugin, including the glimagesink element among others.

The plugin needs the library, but the library can also be used
separately in order to link custom plugins or applications against it.

The library needs at least one OpenGL API, one OpenGL platform and one
compatible window system. The implementations of these requirements that
Buildroot can currently provide are:
 - APIs: OpenGL, OpenGL ES 2.X,
 - platforms: GLX, EGL,
 - window systems: X11, Wayland, Dispmanx.

The wayland configure feature switch is shared between the corresponding
OpenGL library window system and the waylandsink plugin.

This has been tested with videotestsrc/omxmpeg4videodec/omxh264dec and
glimagesink on the Raspberry Pi, using OpenGL ES 2.X, EGL and Dispmanx.

Signed-off-by: Benoît Thébaudeau <benoit@wsystem.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>