cpufreq: powernv: Use cpufreq_frequency_table.driver_data to store pstate ids

The .driver_data field in the cpufreq_frequency_table was supposed to
be private to the drivers. However at some later point, it was being
used to indicate if the particular frequency in the table is the
BOOST_FREQUENCY. After patches [1] and [2], the .driver_data is once
again private to the driver. Thus we can safely use
cpufreq_frequency_table.driver_data to store pstate_ids instead of
having to maintain a separate array powernv_pstate_ids[] for this
purpose.

[1]:
  Subject: cpufreq: don't print value of .driver_data from core
  From   : Viresh Kumar <viresh.kumar@ linaro.org>
  url    : http://marc.info/?l=linux-pm&m=139601421504709&w=2

[2]:
  Subject: cpufreq: create another field .flags in cpufreq_frequency_table
  From   : Viresh Kumar <viresh.kumar@linaro.org>
  url    : http://marc.info/?l=linux-pm&m=139601416804702&w=2Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/powernv-cpufreq.c

@@ -33,7 +33,6 @@
 #define POWERNV_MAX_PSTATES	256
 
 static struct cpufreq_frequency_table powernv_freqs[POWERNV_MAX_PSTATES+1];
-static int powernv_pstate_ids[POWERNV_MAX_PSTATES+1];
 
 /*
  * Note: The set of pstates consists of contiguous integers, the
@@ -112,7 +111,7 @@ static int init_powernv_pstates(void)
 
 		pr_debug("PState id %d freq %d MHz\n", id, freq);
 		powernv_freqs[i].frequency = freq * 1000; /* kHz */
-		powernv_pstate_ids[i] = id;
+		powernv_freqs[i].driver_data = id;
 	}
 	/* End of list marker entry */
 	powernv_freqs[i].frequency = CPUFREQ_TABLE_END;
@@ -283,7 +282,7 @@ static int powernv_cpufreq_target_index(struct cpufreq_policy *policy,
 {
 	struct powernv_smp_call_data freq_data;
 
-	freq_data.pstate_id = powernv_pstate_ids[new_index];
+	freq_data.pstate_id = powernv_freqs[new_index].driver_data;
 
 	/*
 	 * Use smp_call_function to send IPI and execute the