eglfs: Add support for systems without pbuffer support

Use a small native window and window surface in case the hooks indicate
that pbuffer support is not available.

Change-Id: I6515309041f0e1e2f5321d59941f35d6ee16dca7
Reviewed-by: Louai Al-Khanji <louai.al-khanji@digia.com>
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>
Use requestUpdate in QOpenGL and RasterWindow

Change-Id: Ibed4b8d2e2185f1bcf3430932701f81577b59408
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>