drm/qxl: Remove fbcon acceleration leftovers

These are leftovers from 13aff184 ("drm/qxl: remove dead qxl fbdev
emulation code").

v2: Somehow these structs provided the struct qxl_device pre-decl,
reorder the header to not anger compilers.

Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: virtualization@lists.linux-foundation.org
Cc: spice-devel@lists.freedesktop.org
Link: https://patchwork.freedesktop.org/patch/msgid/20201029133347.4088884-1-daniel.vetter@ffwll.ch