irqchip/mmp: Coexist with GIC root IRQ controller

On MMP3, the GIC can be set as a root IRQ interrupt controller. If the
device tree indicated that GIC is enabled, avoid hooking up
mmp2_handle_irq().

The interrupt muxes are still being used.

Signed-off-by: Lubomir Rintel <[e-mail]>
Signed-off-by: Marc Zyngier <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/irqchip/irq-mmp.c

···
 	icu_data[0].conf_disable = mmp3_conf.conf_disable;
 	icu_data[0].conf_mask = mmp3_conf.conf_mask;
 	icu_data[0].conf2_mask = mmp3_conf.conf2_mask;
-	set_handle_irq(mmp2_handle_irq);
+
+	if (!parent) {
+		/* This is the main interrupt controller. */
+		set_handle_irq(mmp2_handle_irq);
+	}
+
 	max_icu_nr = 1;
 	return 0;
 }