m68knommu: add back in declaration of do_IRQ

The cleanup and merge of machdep should not have removed the do_IRQ
declaration. It is needed by the 68328 based targets.
Signed-off-by: Greg Ungerer <gerg@uclinux.org>

arch/m68k/include/asm/machdep.h

@@ -40,5 +40,6 @@ extern unsigned long hw_timer_offset(void);
 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 */