riscv: convert to use arch_cpu_is_hotpluggable()

Convert riscv to use the arch_cpu_is_hotpluggable() helper rather than
arch_register_cpu().
Acked-by: Palmer Dabbelt <palmer@rivosinc.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: Samuel Holland <samuel.holland@sifive.com>
Tested-by: Samuel Holland <samuel.holland@sifive.com> # On HiFive Unmatched
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/E1r5R4L-00Ct0d-To@rmk-PC.armlinux.org.ukSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/riscv/kernel/setup.c

@@ -298,12 +298,9 @@ void __init setup_arch(char **cmdline_p)
 	riscv_user_isa_enable();
 }
 
-int arch_register_cpu(int cpu)
+bool arch_cpu_is_hotpluggable(int cpu)
 {
-	struct cpu *c = &per_cpu(cpu_devices, cpu);
-
-	c->hotpluggable = cpu_has_hotplug(cpu);
-	return register_cpu(c, cpu);
+	return cpu_has_hotplug(cpu);
 }
 
 void free_initmem(void)