drm/ast: Include <linux/of.h> where necessary

Include <linux/of.h> to get of_property_read_u32() in the source
files that need it. Avoids the proxy include via <linux/i2c.h>.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240325200855.21150-2-tzimmermann@suse.de

drivers/gpu/drm/ast/ast_drv.c

@@ -27,6 +27,7 @@
  */
 
 #include <linux/module.h>
+#include <linux/of.h>
 #include <linux/pci.h>
 
 #include <drm/drm_aperture.h>

drivers/gpu/drm/ast/ast_main.c

@@ -26,6 +26,7 @@
  * Authors: Dave Airlie <airlied@redhat.com>
  */
 
+#include <linux/of.h>
 #include <linux/pci.h>
 
 #include <drm/drm_atomic_helper.h>