arm64: convert to arch_cpu_is_hotpluggable()

Convert arm64 to use the arch_cpu_is_hotpluggable() helper rather than
arch_register_cpu().
Reviewed-by: Shaoqin Huang <shahuang@redhat.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Signed-off-by: "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/E1r5R3g-00Cszg-PP@rmk-PC.armlinux.org.ukSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/arm64/kernel/setup.c

@@ -402,13 +402,9 @@ static inline bool cpu_can_disable(unsigned int cpu)
 	return false;
 }
 
-int arch_register_cpu(int num)
+bool arch_cpu_is_hotpluggable(int num)
 {
-	struct cpu *cpu = &per_cpu(cpu_devices, num);
-
-	cpu->hotpluggable = cpu_can_disable(num);
-
-	return register_cpu(cpu, num);
+	return cpu_can_disable(num);
 }
 
 static void dump_kernel_offset(void)