sched/headers: Prepare to remove the <linux/mm_types.h> dependency from <linux/sched.h>

Update code that relied on sched.h including various MM types for them.

This will allow us to remove the <linux/mm_types.h> include from <linux/sched.h>.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/kernel/signal.c b/kernel/signal.c
index e6d470a..2008aa9 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -13,7 +13,7 @@
 #include <linux/slab.h>
 #include <linux/export.h>
 #include <linux/init.h>
-#include <linux/sched.h>
+#include <linux/sched/mm.h>
 #include <linux/sched/user.h>
 #include <linux/sched/debug.h>
 #include <linux/sched/task.h>