The powerpc architecture was the only one that defined
arch_trigger_cpumask_backtrace() in asm/nmi.h instead of
asm/irq.h. Move it to be consistent.

This fixes compile time errors introduced by commit 7ca8fe94
("watchdog/hardlockup: define HARDLOCKUP_DETECTOR_ARCH"). That commit
caused <asm/nmi.h> to stop being included if the hardlockup detector
wasn't enabled. The specific errors were:
  error: implicit declaration of function `nmi_cpu_backtrace'
  error: implicit declaration of function `nmi_trigger_cpumask_backtrace'

NOTE: when moving this into irq.h, we also change the guards from just
checking if "CONFIG_NMI_IPI" is defined to also checking if
"CONFIG_PPC_BOOK3S_64" is defined. This matches the code in
arch/powerpc/kernel/stacktrace.c. Previously this worked because
<asm.nmi.h> was included if "CONFIG_HAVE_HARDLOCKUP_DETECTOR_ARCH" was
defined. For powerpc that's only selected if "CONFIG_PPC_BOOK3S_64" is
defined.

[dianders@chromium.org: change the guards to include CONFIG_PPC_BOOK3S_64]
  Link: https://lkml.kernel.org/r/20230622202816.v2.1.Ice67126857506712559078e7de26d32d26e64631@changeid
Link: https://lkml.kernel.org/r/20230621164809.1.Ice67126857506712559078e7de26d32d26e64631@changeid
Fixes: 7ca8fe94 ("watchdog/hardlockup: define HARDLOCKUP_DETECTOR_ARCH")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Closes: https://lore.kernel.org/r/871qi5otdh.fsf@mail.lhotseReviewed-by: Petr Mladek <pmladek@suse.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Douglas Anderson <dianders@chromium.org>
Cc: Laurent Dufour <ldufour@linux.ibm.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Tom Rix <trix@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>