drm/mga: drop use of drmP.h

Drop the use of the deprecated drmP.h header file.
Clean up list of include files and sort them.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@linux.ie>
Link: https://patchwork.freedesktop.org/patch/msgid/20190623103542.30697-4-sam@ravnborg.org

drivers/gpu/drm/mga/mga_state.c

@@ -32,8 +32,6 @@
  *    Gareth Hughes <gareth@valinux.com>
  */
 
-#include <drm/drmP.h>
-#include <drm/mga_drm.h>
 #include "mga_drv.h"
 
 /* ================================================================