sched/headers: Prepare for new header dependencies before moving code to <linux/sched/nmi.h>

We are going to move softlockup APIs out of <linux/sched.h>, which
will have to be picked up from other headers and a couple of .c files.

<linux/nmi.h> already includes <linux/sched.h>.

Include the <linux/nmi.h> header in the files that are going to need it.

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/init/main.c b/init/main.c
index ae9f200..c891cfb 100644
--- a/init/main.c
+++ b/init/main.c
@@ -27,6 +27,7 @@
 #include <linux/bootmem.h>
 #include <linux/acpi.h>
 #include <linux/tty.h>
+#include <linux/nmi.h>
 #include <linux/percpu.h>
 #include <linux/kmod.h>
 #include <linux/vmalloc.h>