drm: fixed: Don't use "proxy" headers

Update header inclusions to follow IWYU (Include What You Use)
principle.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240422143338.2026791-1-andriy.shevchenko@linux.intel.comSigned-off-by: Jani Nikula <jani.nikula@intel.com>

include/drm/drm_fixed.h

@@ -25,8 +25,9 @@
 #ifndef DRM_FIXED_H
 #define DRM_FIXED_H
 
-#include <linux/kernel.h>
 #include <linux/math64.h>
+#include <linux/types.h>
+#include <linux/wordpart.h>
 
 typedef union dfixed {
 	u32 full;