NPOT texture support in QOpenGLTextureCache

Enable non power of two texture support for non compatible NPOT GPU.
If the context does not handle NPOTTexture feature, the image to bind is scaled to POT size. It works with OpenGL ES and Desktop version.
It is actually almost the same code as the one in QGLContextPrivate::bindTexture.

Change-Id: I6f0f511165c9e171a14f4ba6ba0b7a902e590cf6
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>