staging: vboxvideo: Stop disabling/enabling accel support on master set / drop

Userspace mode-setting (and thus also VESA) is not supported together with
modesetting. KMS userspace apps not properly marking the framebuffer as
dirty are also not supported.

So stop trying to accommodate this and simply enable accel
once at driver init.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>