powerpc: 52xx: nop out unsupported critical IRQs

Currently, when booting MPC52xx based platforms, we get:

        mpc52xx_irqhost_map: invalid irq: virq=16, l1=0, l2=3
        irq: irq-16==>hwirq-0x3 mapping failed: -22
        [WARNing skipped]

The warning is wrong since the mapping itself is valid. However, there is no
support for that type of IRQ currently. Print a proper warning and bind the irq
to a no_irq chip.
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Cc: John Bonesio <bones@secretlab.ca>
Cc: Anatolij Gustschin <agust@denx.de>
Cc: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Anatolij Gustschin <agust@denx.de>

arch/powerpc/platforms/52xx/mpc52xx_pic.c

@@ -372,10 +372,11 @@ static int mpc52xx_irqhost_map(struct irq_domain *h, unsigned int virq,
 	case MPC52xx_IRQ_L1_MAIN: irqchip = &mpc52xx_main_irqchip; break;
 	case MPC52xx_IRQ_L1_PERP: irqchip = &mpc52xx_periph_irqchip; break;
 	case MPC52xx_IRQ_L1_SDMA: irqchip = &mpc52xx_sdma_irqchip; break;
-	default:
-		pr_err("%s: invalid irq: virq=%i, l1=%i, l2=%i\n",
-		       __func__, virq, l1irq, l2irq);
-		return -EINVAL;
+	case MPC52xx_IRQ_L1_CRIT:
+		pr_warn("%s: Critical IRQ #%d is unsupported! Nopping it.\n",
+			__func__, l2irq);
+		irq_set_chip(virq, &no_irq_chip);
+		return 0;
 	}
 
 	irq_set_chip_and_handler(virq, irqchip, handle_level_irq);