QNX: Enable threaded OpenGL rendering on QNX

QNX: Enable threaded OpenGL rendering on QNX

The only complicated aspect to this was deferring EGLsurface
re-creation as a result of window geometry changes (e.g. when we
receive an orientation change event). To allow this to be done
in a controlled way we defer the surface manipulation until the
next call to QQnxGLContext::makeCurrent().

Change-Id: I8062d3e4d19220a822fbc3b8ca563bb1e3be09d0
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>
Reviewed-by: Kevin Krammer <kevin.krammer@kdab.com>
Reviewed-by: Thomas McGuire <thomas.mcguire@kdab.com>
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>