eglimagememory: Methods to create GstGLMemory from dmabufs

eglimagememory: Methods to create GstGLMemory from dmabufs

Maps GstVideoFormats to suitable DRM fourccs which work with
glcolorconvert, using gst_gl_memory_alloc(). We require mostly
only 4 formats to be supported by the driver. We require DRM
equivalent to RGB16, RGBA, R8 and RG88. This way it's compatible with
DesktopGL, since GL_TEXTURE_2D is used and limit driver requirements.
With this we can virtually support all formats the glcolorconvert
supports.

https://bugzilla.gnome.org/show_bug.cgi?id=743345