drm/via: drop use of drmP.h

Drop use of the deprecated drmP.h header.
While touching the files divide include files in blocks
and sort the files alphabetically.

v2:
- Replace all uses of DRM_WAIT_ON() with VIA_WAIT_ON()
  and thus avoiding to pull in drm_os_linux.h

v3:
- DRM_WAIT_ON replacement moved to earlier patch (Emil)

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Cc: Kevin Brace <kevinbrace@gmx.com>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Cc: Mike Marshall <hubcap@omnibond.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Michel Dänzer <michel@daenzer.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20190723200944.17285-5-sam@ravnborg.org

drivers/gpu/drm/via/via_mm.c

@@ -25,8 +25,13 @@
  * Authors: Thomas Hellström <thomas-at-tungstengraphics-dot-com>
  */
 
-#include <drm/drmP.h>
+#include <linux/slab.h>
+
+#include <drm/drm_device.h>
+#include <drm/drm_file.h>
+#include <drm/drm_irq.h>
 #include <drm/via_drm.h>
+
 #include "via_drv.h"
 
 #define VIA_MM_ALIGN_SHIFT 4