powerpc: Add struct smp_ops_t.cause_nmi_ipi operation

Have the NMI IPI code use this op when the platform defines it.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/smp.h

@@ -42,6 +42,7 @@ struct smp_ops_t {
 #ifdef CONFIG_PPC_SMP_MUXED_IPI
 	void  (*cause_ipi)(int cpu);
 #endif
+	int   (*cause_nmi_ipi)(int cpu);
 	void  (*probe)(void);
 	int   (*kick_cpu)(int nr);
 	int   (*prepare_cpu)(int nr);