drm/virtgpu: drop use of drmP.h

Drop use of the deprecated drmP.h header file.
Fix fallout by adding missing include files.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Emil Velikov <emil.velikov@collabora.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: virtualization@lists.linux-foundation.org
Link: https://patchwork.freedesktop.org/patch/msgid/20190630061922.7254-28-sam@ravnborg.org