arm64: smp: make local symbol static

Make smp_spin_table_cpu_postboot() static, because this function
is used only in this file.
Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/smp_spin_table.c

@@ -128,7 +128,7 @@ static int smp_spin_table_cpu_boot(unsigned int cpu)
 	return secondary_holding_pen_release != INVALID_HWID ? -ENOSYS : 0;
 }
 
-void smp_spin_table_cpu_postboot(void)
+static void smp_spin_table_cpu_postboot(void)
 {
 	/*
 	 * Let the primary processor know we're out of the pen.