ARM: GIC: function to retrieve the physical address of the SGIR

In order to have early assembly code signal other CPUs in the system,
we need to get the physical address for the SGIR register used to
send IPIs.  Because the register will be used with a precomputed CPU
interface ID number, there is no need for any locking in the assembly
code where this register is written to.

Signed-off-by: Nicolas Pitre <nico@linaro.org>

include/linux/irqchip/arm-gic.h

@@ -78,6 +78,7 @@ static inline void gic_init(unsigned int nr, int start,
 
 int gic_get_cpu_id(unsigned int cpu);
 void gic_migrate_target(unsigned int new_cpu_id);
+unsigned long gic_get_sgir_physaddr(void);
 
 #endif /* __ASSEMBLY */