LoongArch: convert to use arch_cpu_is_hotpluggable()

Convert loongarch to use the arch_cpu_is_hotpluggable() helper rather
than arch_register_cpu(). Also remove the export as nothing should be
using arch_register_cpu() outside of the core kernel/acpi code.
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/E1r5R4B-00Ct0G-Kk@rmk-PC.armlinux.org.ukSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/loongarch/kernel/topology.c

@@ -11,11 +11,8 @@
 #include <acpi/processor.h>
 
 #ifdef CONFIG_HOTPLUG_CPU
-int arch_register_cpu(int cpu)
+bool arch_cpu_is_hotpluggable(int cpu)
 {
-	struct cpu *c = &per_cpu(cpu_devices, cpu);
-
-	c->hotpluggable = !io_master(cpu);
-	return register_cpu(c, cpu);
+	return !io_master(cpu);
 }
 #endif