ARM: 6000/1: removing compilation warning comming from <asm/irq.h>

irq.h is using struct pt_regs *. Due to this compilation
warning is comming. Removing this warning by adding declaration
of struct pt_regs.
Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/include/asm/irq.h

@@ -17,6 +17,7 @@
 
 #ifndef __ASSEMBLY__
 struct irqaction;
+struct pt_regs;
 extern void migrate_irqs(void);
 
 extern void asm_do_IRQ(unsigned int, struct pt_regs *);