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>

arch/mips/include/asm/mach-generic/irq.h

@@ -18,7 +18,7 @@
 #endif
 #endif
 
-#ifdef CONFIG_IRQ_CPU
+#ifdef CONFIG_IRQ_MIPS_CPU
 
 #ifndef MIPS_CPU_IRQ_BASE
 #ifdef CONFIG_I8259
@@ -34,7 +34,7 @@
 #endif
 #endif
 
-#endif /* CONFIG_IRQ_CPU */
+#endif /* CONFIG_IRQ_MIPS_CPU */
 
 #ifdef CONFIG_MIPS_GIC
 #ifndef MIPS_GIC_IRQ_BASE