irqchip: add C-SKY APB bus interrupt controller

The driver is for C-SKY APB bus interrupt controller. It's a simple
interrupt controller which use pending reg to detect the irq and use
enable/disable reg to mask/unmask interrupt sources.

A lot of SOCs based on C-SKY CPU use the interrupt controller as root
controller.

Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
diff --git a/drivers/irqchip/Makefile b/drivers/irqchip/Makefile
index 6b739ea..72eaf53 100644
--- a/drivers/irqchip/Makefile
+++ b/drivers/irqchip/Makefile
@@ -88,4 +88,5 @@
 obj-$(CONFIG_NDS32)			+= irq-ativic32.o
 obj-$(CONFIG_QCOM_PDC)			+= qcom-pdc.o
 obj-$(CONFIG_CSKY_MPINTC)		+= irq-csky-mpintc.o
+obj-$(CONFIG_CSKY_APB_INTC)		+= irq-csky-apb-intc.o
 obj-$(CONFIG_SIFIVE_PLIC)		+= irq-sifive-plic.o