Support EGLStream in wayland-egl

For Wayland on NVIDIA. Tested with a Jetson TK1 Pro and Vibrante Linux.

With just the hw integration no compositors would work out of the box
since EGL_KHR_stream_consumer_gltexture only allows connecting to the
texture bound to GL_TEXTURE_EXTERNAL_OES, meaning that assumptions about
the target always being GL_TEXTURE_2D break horribly both in C++ and in
shader code.

In addition, buffers have to be extended with an additional updateTexture()
operation as EGLStream requires to call ConsumerAcquire on every
frame. Previously there was no concept of this as calling
createTexture() on attach() was sufficient.

Qt Quick bits are omitted since the refactored compositor API is pretty
different. This means that QML compositors will not currently function
in this environment.

The qwindow-compositor example is enhanced to support the external
texture target, but this won't apply for the refactored branch
either. It is provided for testing purposes for the time being, and to
show how C++ compositors can support different texture targets and
correct operation with EGLStreams.

Done-with: Louai Al-Khanji <louai.al-khanji@theqtcompany.com>
Change-Id: I0e209fc0cbcf435cca83528d938eb50e4bdceb82
Reviewed-by: Louai Al-Khanji <louai.al-khanji@theqtcompany.com>