m68knommu: Move forward declaration of do_IRQ() from machdep.h to irq.h

It is not machine-specific, but common irq infrastructure.
Also add the missing asmlinkage, to match its definition.

Signed-off-by: Geert Uytterhoeven <[e-mail]>
Signed-off-by: Greg Ungerer <[e-mail]>

arch/m68k/include/asm/irq.h

···
 #define irq_canonicalize(irq)  (irq)
 #endif /* CONFIG_MMU */
 
+asmlinkage void do_IRQ(int irq, struct pt_regs *regs);
+
 #endif /* _M68K_IRQ_H_ */

arch/m68k/include/asm/machdep.h

···
 extern irqreturn_t arch_timer_interrupt(int irq, void *dummy);
 
 extern void config_BSP(char *command, int len);
-extern void do_IRQ(int irq, struct pt_regs *fp);
 
 #endif /* _M68K_MACHDEP_H */