powerpc: Add kconfig for muxed smp ipi support

Compile the new smp ipi mux and demux code only if a platform
will make use of it.  The new config is selected as required.

The new cause_ipi smp op is only available conditionally to point out
configs where the select is required; this makes setting the op an
immediate fail instead of a deferred unresolved symbol at link.

This also creates a new config for power surge powermac upgrade support
that can be disabled in expert mode but is default on.

I also removed the depends / default y on CONFIG_XICS since it is selected
by PSERIES.

Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/smp.c

@@ -178,6 +178,7 @@ int smp_request_message_ipi(int virq, int msg)
 	return err;
 }
 
+#ifdef CONFIG_PPC_SMP_MUXED_IPI
 struct cpu_messages {
 	unsigned long messages;		/* current messages bits */
 	unsigned long data;		/* data for cause ipi */
@@ -230,6 +231,7 @@ irqreturn_t smp_ipi_demux(void)
 	}
 	return IRQ_HANDLED;
 }
+#endif /* CONFIG_PPC_SMP_MUXED_IPI */
 
 void smp_send_reschedule(int cpu)
 {