ARC: smp: irqchip: handle IPI as percpu irq like timer

The reason this was not done so far was lack of genuine IPI_IRQ for
ARC700, as we don't have a SMP version of core yet (which might change
soon thx to EZChip). Nevertheles to increase the build coverage, we
need to allow CONFIG_SMP for ARC700 and still be able to run it on a
UP platform (nsim or AXS101) with a UP Device Tree (SMP-on-UP)

The build itself requires some define for IPI_IRQ and even a dummy
value is fine since that code won't run anyways.
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/include/asm/irq.h

@@ -16,6 +16,7 @@
 #ifdef CONFIG_ISA_ARCOMPACT
 #define TIMER0_IRQ      3
 #define TIMER1_IRQ      4
+#define IPI_IRQ		(NR_CPU_IRQS-1) /* dummy to enable SMP build for up hardware */
 #else
 #define TIMER0_IRQ      16
 #define TIMER1_IRQ      17

arch/arc/kernel/intc-compact.c

@@ -79,17 +79,16 @@ static struct irq_chip onchip_intc = {
 static int arc_intc_domain_map(struct irq_domain *d, unsigned int irq,
 			       irq_hw_number_t hw)
 {
-	/*
-	 * XXX: the IPI IRQ needs to be handled like TIMER too. However ARC core
-	 *      code doesn't own it (like TIMER0). ISS IDU / ezchip define it
-	 *      in platform header which can't be included here as it goes
-	 *      against multi-platform image philisophy
-	 */
-	if (irq == TIMER0_IRQ)
+	switch (irq) {
+	case TIMER0_IRQ:
+#ifdef CONFIG_SMP
+	case IPI_IRQ:
+#endif
 		irq_set_chip_and_handler(irq, &onchip_intc, handle_percpu_irq);
-	else
+		break;
+	default:
 		irq_set_chip_and_handler(irq, &onchip_intc, handle_level_irq);
-
+	}
 	return 0;
 }