arm64: psci: fix !CONFIG_HOTPLUG_CPU build warning

When building without CONFIG_HOTPLUG_CPU, GCC complains (rightly) that
psci_tos_resident_on is unused:

  arch/arm64/kernel/psci.c:61:13: warning: ‘psci_tos_resident_on’ defined but not used [-Wunused-function]
   static bool psci_tos_resident_on(int cpu)

As it's only ever used when CONFIG_HOTPLUG_CPU is selected, let's move
it into the existing ifdef.
Signed-off-by: Will Deacon <will.deacon@arm.com>
[Mark: write commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/psci.c

@@ -58,11 +58,6 @@ static bool psci_power_state_is_valid(u32 state)
  */
 static int resident_cpu = -1;
 
-static bool psci_tos_resident_on(int cpu)
-{
-	return cpu == resident_cpu;
-}
-
 struct psci_operations {
 	int (*cpu_suspend)(u32 state, unsigned long entry_point);
 	int (*cpu_off)(u32 state);
@@ -494,6 +489,11 @@ static int cpu_psci_cpu_boot(unsigned int cpu)
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
+static bool psci_tos_resident_on(int cpu)
+{
+	return cpu == resident_cpu;
+}
+
 static int cpu_psci_cpu_disable(unsigned int cpu)
 {
 	/* Fail early if we don't have CPU_OFF support */