[MIPS] Define MIPS_CPU_IRQ_BASE in generic header

The irq_base for {mips,rm7k,rm9k}_cpu_irq_init() are constant on all
platforms and are same value on most platforms (0 or 16, depends on
CONFIG_I8259).  Define them in asm-mips/mach-generic/irq.h and make
them customizable.  This will save a few cycle on each CPU interrupt.

A good side effect is removing some dependencies to MALTA in generic
SMTC code.

Although MIPS_CPU_IRQ_BASE is customizable, this patch changes irq
mappings on DDB5477, EMMA2RH and MIPS_SIM, since really customizing
them might cause some header dependency problem and there seems no
good reason to customize it.  So currently only VR41XX is using custom
MIPS_CPU_IRQ_BASE value, which is 0 regardless of CONFIG_I8259.

Testing this patch on those platforms is greatly appreciated.  Thank
you.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/ddb5xxx/ddb5477/irq.c b/arch/mips/ddb5xxx/ddb5477/irq.c
index a8bd2e6..bd7cd7c 100644
--- a/arch/mips/ddb5xxx/ddb5477/irq.c
+++ b/arch/mips/ddb5xxx/ddb5477/irq.c
@@ -17,6 +17,7 @@
 #include <linux/ptrace.h>
 
 #include <asm/i8259.h>
+#include <asm/irq_cpu.h>
 #include <asm/system.h>
 #include <asm/mipsregs.h>
 #include <asm/debug.h>
@@ -73,7 +74,6 @@
 }
 
 extern void vrc5477_irq_init(u32 base);
-extern void mips_cpu_irq_init(u32 base);
 static struct irqaction irq_cascade = { no_action, 0, CPU_MASK_NONE, "cascade", NULL, NULL };
 
 void __init arch_init_irq(void)
@@ -125,7 +125,7 @@
 
 	/* init all controllers */
 	init_i8259_irqs();
-	mips_cpu_irq_init(CPU_IRQ_BASE);
+	mips_cpu_irq_init();
 	vrc5477_irq_init(VRC5477_IRQ_BASE);