drm: Include <linux/of.h> where needed

Include <linux/of.h> in source files that need it. Some of DRM's
source code gets OF header via drm_crtc_helper.h and <linux/fb.h>,
which can leed to unnecessary recompilation.

In drm_modes.c, add a comment on the reason for still including
<linux/fb.h>. The header file is required to get KHZ2PICOS(). The
macro is part of the UAPI headers, so it cannot be moved to a less
prominent location.

v2:
	* include <linux/of.h> in komeda_drv.c (kernel test robot)
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Liviu Dudau <liviu.dudau@arm.com> # komeda
Acked-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20230111130206.29974-3-tzimmermann@suse.de

drivers/gpu/drm/arm/display/komeda/komeda_drv.c

@@ -6,6 +6,7 @@
  */
 #include <linux/module.h>
 #include <linux/kernel.h>
+#include <linux/of.h>
 #include <linux/platform_device.h>
 #include <linux/component.h>
 #include <linux/pm_runtime.h>

drivers/gpu/drm/drm_modes.c

@@ -31,10 +31,11 @@
  */
 
 #include <linux/ctype.h>
+#include <linux/export.h>
+#include <linux/fb.h> /* for KHZ2PICOS() */
 #include <linux/list.h>
 #include <linux/list_sort.h>
-#include <linux/export.h>
-#include <linux/fb.h>
+#include <linux/of.h>
 
 #include <video/of_display_timing.h>
 #include <video/of_videomode.h>

drivers/gpu/drm/panel/panel-ronbo-rb070d30.c

@@ -15,6 +15,7 @@
 #include <linux/kernel.h>
 #include <linux/media-bus-format.h>
 #include <linux/module.h>
+#include <linux/of.h>
 
 #include <linux/gpio/consumer.h>
 #include <linux/regulator/consumer.h>