MIPS: Fix warning when including smp-ops.h with CONFIG_SMP=n

The gic_send_ipi_mask function declared in smp-ops.h takes a struct
cpumask argument, but linux/cpumask.h is only included within an #ifdef
CONFIG_SMP. Move the gic_ function declarations within that #ifdef too
to fix warnings during build such as:

In file included from arch/mips/fw/arc/init.c:15:0:
/mnt/buildbot/kernel/mips/slave/mips-linux__allno_/build/arch/mips/include/asm/smp-ops.h:62:44:
warning: 'struct cpumask' declared inside parameter list [enabled by
default]
 extern void gic_send_ipi_mask(const struct cpumask *mask, unsigned int
action);
Reported-by: Markos Chandras <markos.chandras@imgtec.com>
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/6655/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/smp-ops.h

@@ -45,6 +45,9 @@ static inline void plat_smp_setup(void)
 	mp_ops->smp_setup();
 }
 
+extern void gic_send_ipi_single(int cpu, unsigned int action);
+extern void gic_send_ipi_mask(const struct cpumask *mask, unsigned int action);
+
 #else /* !CONFIG_SMP */
 
 struct plat_smp_ops;
@@ -60,9 +63,6 @@ static inline void register_smp_ops(struct plat_smp_ops *ops)
 
 #endif /* !CONFIG_SMP */
 
-extern void gic_send_ipi_single(int cpu, unsigned int action);
-extern void gic_send_ipi_mask(const struct cpumask *mask, unsigned int action);
-
 static inline int register_up_smp_ops(void)
 {
 #ifdef CONFIG_SMP_UP