opengl: move shader init from console-gl.c to shader.c

With the upcoming dmabuf support in qemu there will be more users of the
shaders than just console-gl.c.  So rename ConsoleGLState to
QemuGLShader, rename some functions too, move code from console-gl.c to
shaders.c.

No functional change.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 20171010135453.6704-3-kraxel@redhat.com