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/kernel/smpboot.c

@@ -1376,12 +1376,12 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
 	speculative_store_bypass_ht_init();
 }
 
-void arch_enable_nonboot_cpus_begin(void)
+void arch_thaw_secondary_cpus_begin(void)
 {
 	set_mtrr_aps_delayed_init();
 }
 
-void arch_enable_nonboot_cpus_end(void)
+void arch_thaw_secondary_cpus_end(void)
 {
 	mtrr_aps_init();
 }