powerpc: Include asm/nmi.c in mobility.c for watchdog_hardlockup_set_timeout_pct()

The powerpc/platforms/pseries/mobility.c calls
watchdog_hardlockup_set_timeout_pct(), which is declared in
<asm/nmi.h>. We used to automatically get <asm/nmi.h> included, but
that changed as of commit 7ca8fe94 ("watchdog/hardlockup: define
HARDLOCKUP_DETECTOR_ARCH"). Let's add the explicit include.
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Closes: https://lore.kernel.org/r/af19b76d-aa4b-6c88-9cac-eae4b2072497@infradead.org
Fixes: 7ca8fe94 ("watchdog/hardlockup: define HARDLOCKUP_DETECTOR_ARCH")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230629124500.1.I55e2f4e7903d686c4484cb23c033c6a9e1a9d4c4@changeid

arch/powerpc/platforms/pseries/mobility.c

@@ -24,6 +24,7 @@
 #include <linux/stringify.h>
 
 #include <asm/machdep.h>
+#include <asm/nmi.h>
 #include <asm/rtas.h>
 #include "pseries.h"
 #include "vas.h"	/* vas_migration_handler() */