cpu/hotplug: Remove disable_nonboot_cpus()

The single user could have called freeze_secondary_cpus() directly.

Since this function was a source of confusion, remove it as it's
just a pointless wrapper.

While at it, rename enable_nonboot_cpus() to thaw_secondary_cpus() to
preserve the naming symmetry.

Done automatically via:

	git grep -l enable_nonboot_cpus | xargs sed -i 's/enable_nonboot_cpus/thaw_secondary_cpus/g'

Signed-off-by: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Link: https://lkml.kernel.org/r/20200430114004.17477-1-qais.yousef@arm.com

arch/x86/power/cpu.c

@@ -307,7 +307,7 @@ int hibernate_resume_nonboot_cpu_disable(void)
 	if (ret)
 		return ret;
 	smp_ops.play_dead = resume_play_dead;
-	ret = disable_nonboot_cpus();
+	ret = freeze_secondary_cpus(0);
 	smp_ops.play_dead = play_dead;
 	return ret;
 }