[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>

include/asm-mips/ddb5xxx/ddb5477.h

@@ -17,6 +17,7 @@
 #ifndef __ASM_DDB5XXX_DDB5477_H
 #define __ASM_DDB5XXX_DDB5477_H
 
+#include <irq.h>
 
 /*
  * This contains macros that are specific to DDB5477 or renamed from
@@ -257,8 +258,8 @@ extern void ll_vrc5477_irq_disable(int vrc5477_irq);
 #define	DDB_IRQ_BASE		0
 
 #define	I8259_IRQ_BASE		DDB_IRQ_BASE
-#define	VRC5477_IRQ_BASE	(I8259_IRQ_BASE + NUM_I8259_IRQ)
-#define	CPU_IRQ_BASE		(VRC5477_IRQ_BASE + NUM_VRC5477_IRQ)
+#define	CPU_IRQ_BASE		MIPS_CPU_IRQ_BASE
+#define	VRC5477_IRQ_BASE	(CPU_IRQ_BASE + NUM_CPU_IRQ)
 
 /*
  * vrc5477 irq defs