powerpc: Fix HAVE_HARDLOCKUP_DETECTOR_ARCH build configuration

When compiling the powerpc with the SMP disabled, it shows the issue:

arch/powerpc/kernel/watchdog.c: In function ‘watchdog_smp_panic’:
arch/powerpc/kernel/watchdog.c:177:4: error: implicit declaration of function ‘smp_send_nmi_ipi’; did you mean ‘smp_send_stop’? [-Werror=implicit-function-declaration]
  177 |    smp_send_nmi_ipi(c, wd_lockup_ipi, 1000000);
      |    ^~~~~~~~~~~~~~~~
      |    smp_send_stop
cc1: all warnings being treated as errors
make[2]: *** [scripts/Makefile.build:273: arch/powerpc/kernel/watchdog.o] Error 1
make[1]: *** [scripts/Makefile.build:534: arch/powerpc/kernel] Error 2
make: *** [Makefile:1980: arch/powerpc] Error 2
make: *** Waiting for unfinished jobs....

We found that powerpc used ipi to implement hardlockup watchdog, so the
HAVE_HARDLOCKUP_DETECTOR_ARCH should depend on the SMP.

Fixes: 2104180a53 ("powerpc/64s: implement arch-specific hardlockup watchdog")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Chen Huang <chenhuang5@huawei.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210327094900.938555-1-chenhuang5@huawei.com

arch/powerpc/Kconfig

@@ -226,7 +226,7 @@ config PPC
 	select HAVE_LIVEPATCH			if HAVE_DYNAMIC_FTRACE_WITH_REGS
 	select HAVE_MOD_ARCH_SPECIFIC
 	select HAVE_NMI				if PERF_EVENTS || (PPC64 && PPC_BOOK3S)
-	select HAVE_HARDLOCKUP_DETECTOR_ARCH	if (PPC64 && PPC_BOOK3S)
+	select HAVE_HARDLOCKUP_DETECTOR_ARCH	if PPC64 && PPC_BOOK3S && SMP
 	select HAVE_OPTPROBES			if PPC64
 	select HAVE_PERF_EVENTS
 	select HAVE_PERF_EVENTS_NMI		if PPC64