MIPS/IRQCHIP: Move irq_chip from arch/mips to drivers/irqchip.

While at it, rename it because in drivers/irqchip no longer every CPU is
a MIPS.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/drivers/irqchip/Kconfig b/drivers/irqchip/Kconfig
index 6de62a9..2b7531e 100644
--- a/drivers/irqchip/Kconfig
+++ b/drivers/irqchip/Kconfig
@@ -85,6 +85,11 @@
 	select GENERIC_IRQ_CHIP
 	select IRQ_DOMAIN
 
+config IRQ_MIPS_CPU
+	bool
+	select GENERIC_IRQ_CHIP
+	select IRQ_DOMAIN
+
 config CLPS711X_IRQCHIP
 	bool
 	depends on ARCH_CLPS711X