drm: remove include of drmP.h from bridge/dw_hdmi.h

drmP.h is an relic from the days when there was a single header file.
To enable the removal of drmP.h from all users drop include
of drmP.h from bridge/dw_hdmi.h.

A few files relied on the file included in drmP.h - add explicit
include statements or forward declarations to these files.
Build tested with arm and x86.

v2:
- prefer forward declarations when possible (Laurent Pinchart)
- sort include files (Laurent Pinchart)
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Archit Taneja <architt@codeaurora.org>
Cc: Andrzej Hajda <a.hajda@samsung.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Cc: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20190108192939.15255-7-sam@ravnborg.org

drivers/gpu/drm/bridge/synopsys/dw-hdmi-i2s-audio.c

@@ -5,6 +5,10 @@
  * Copyright (c) 2017 Renesas Solutions Corp.
  * Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
  */
+
+#include <linux/dma-mapping.h>
+#include <linux/module.h>
+
 #include <drm/bridge/dw_hdmi.h>
 
 #include <sound/hdmi-codec.h>

drivers/gpu/drm/rcar-du/rcar_dw_hdmi.c

@@ -7,6 +7,7 @@
  * Contact: Laurent Pinchart (laurent.pinchart@ideasonboard.com)
  */
 
+#include <linux/mod_devicetable.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>
 

include/drm/bridge/dw_hdmi.h

@@ -10,9 +10,11 @@
 #ifndef __DW_HDMI__
 #define __DW_HDMI__
 
-#include <drm/drmP.h>
-
+struct drm_connector;
+struct drm_display_mode;
+struct drm_encoder;
 struct dw_hdmi;
+struct platform_device;
 
 /**
  * DOC: Supported input formats and encodings