cpufreq: CPPC: Fix unused-function warning

Building the cppc_cpufreq driver with for arm64 with
CONFIG_ENERGY_MODEL=n triggers the following warnings:
 drivers/cpufreq/cppc_cpufreq.c:550:12: error: ‘cppc_get_cpu_cost’ defined but not used
[-Werror=unused-function]
   550 | static int cppc_get_cpu_cost(struct device *cpu_dev, unsigned long KHz,
       |            ^~~~~~~~~~~~~~~~~
 drivers/cpufreq/cppc_cpufreq.c:481:12: error: ‘cppc_get_cpu_power’ defined but not used
[-Werror=unused-function]
   481 | static int cppc_get_cpu_power(struct device *cpu_dev,
       |            ^~~~~~~~~~~~~~~~~~

Move the Energy Model related functions into specific guards.
This allows to fix the warning and prevent doing extra work
when the Energy Model is not present.

Fixes: 740fcdc2 ("cpufreq: CPPC: Register EM based on efficiency class information")
Reported-by: Shaokun Zhang <zhangshaokun@hisilicon.com>
Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Tested-by: Shaokun Zhang <zhangshaokun@hisilicon.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/cppc_cpufreq.c

@@ -441,6 +441,14 @@ static unsigned int cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
 	}
 	return cppc_get_transition_latency(cpu) / NSEC_PER_USEC;
 }
+#else
+static unsigned int cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
+{
+	return cppc_get_transition_latency(cpu) / NSEC_PER_USEC;
+}
+#endif
+
+#if defined(CONFIG_ARM64) && defined(CONFIG_ENERGY_MODEL)
 
 static DEFINE_PER_CPU(unsigned int, efficiency_class);
 static void cppc_cpufreq_register_em(struct cpufreq_policy *policy);
@@ -621,21 +629,12 @@ static void cppc_cpufreq_register_em(struct cpufreq_policy *policy)
 }
 
 #else
-
-static unsigned int cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
-{
-	return cppc_get_transition_latency(cpu) / NSEC_PER_USEC;
-}
 static int populate_efficiency_class(void)
 {
 	return 0;
 }
-static void cppc_cpufreq_register_em(struct cpufreq_policy *policy)
-{
-}
 #endif
 
-
 static struct cppc_cpudata *cppc_cpufreq_get_cpu_data(unsigned int cpu)
 {
 	struct cppc_cpudata *cpu_data;