Wayland support for EGLStream

Current situation is as follows:

• For an introduction see the blog post http://blog.qt.io/blog/2015/11/17/embedded-linux-news-in-qt-5-6/

• This means that in Qt Wayland 5.6 we have full support for the Jetson with the old C++ APIs. On the other hand, there is no support at all for the Qt Quick (QML) APIs. There are no plans the make the latter work since this branch (the old compositor API) is soon irrelevant.

• With Qt Wayland dev (earlier known as wip-compositor-api) branch (that will become 5.7) we have a half-broken merge from 5.6 that includes the basic enablers. Neither the C++ nor the QML APIs are functional on the Jetson at this stage.

• See this open patch https://codereview.qt-project.org/#/c/139180/ and the comments regarding the current issues. This tries to bring the new C++ compositor API into a usable state on the Jetson.

• Once the C++ APIs are usable, QML is a completely separate story. This is because EGLStreams involve using texture targets other than GL_TEXTURE_2D to which the infrastructure is not prepared at all. There is an (abandoned) patch against 5.4 that can be used as an inspiration for the QML bits. However, the way QWaylandSurfaceItem is changed there is not ideal (it really should not be an FBO) and will anyway not apply to the new branch at all.

So in short, the following needs to be done:

1. Make https://codereview.qt-project.org/#/c/139180/ work and get it in.

2. Come up with a solution that allows using GL_TEXTURE_EXTERNAL_OES textures in Qt Quick compositors.