drm/scheduler: Include <linux/export.h>

Fix the compile-time warnings

  drivers/gpu/drm/scheduler/sched_entity.c: warning: EXPORT_SYMBOL() is used, but #include <linux/export.h> is missing
  drivers/gpu/drm/scheduler/sched_fence.c: warning: EXPORT_SYMBOL() is used, but #include <linux/export.h> is missing
  drivers/gpu/drm/scheduler/sched_main.c: warning: EXPORT_SYMBOL() is used, but #include <linux/export.h> is missing

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: a934a57a42 ("scripts/misc-check: check missing #include <linux/export.h> when W=1")
Reviewed-by: André Almeida <andrealmeid@igalia.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20250612121633.229222-9-tzimmermann@suse.de

drivers/gpu/drm/scheduler/sched_entity.c

@@ -21,6 +21,7 @@
  *
  */
 
+#include <linux/export.h>
 #include <linux/slab.h>
 #include <linux/completion.h>
 

drivers/gpu/drm/scheduler/sched_fence.c

@@ -21,6 +21,7 @@
  *
  */
 
+#include <linux/export.h>
 #include <linux/module.h>
 #include <linux/sched.h>
 #include <linux/slab.h>

drivers/gpu/drm/scheduler/sched_main.c

@@ -66,6 +66,7 @@
  * This implies waiting for previously executed jobs.
  */
 
+#include <linux/export.h>
 #include <linux/wait.h>
 #include <linux/sched.h>
 #include <linux/completion.h>