cpufreq: powernv: fix stack bloat and hard limit on number of CPUs

The following build warning occurred on powerpc 64-bit builds:

drivers/cpufreq/powernv-cpufreq.c: In function 'init_chip_info':
drivers/cpufreq/powernv-cpufreq.c:1070:1: warning: the frame size of
1040 bytes is larger than 1024 bytes [-Wframe-larger-than=]

This is with a cross-compiler based on gcc 8.1.0, which I got from:
  https://mirrors.edge.kernel.org/pub/tools/crosstool/files/bin/x86_64/8.1.0/

The warning is due to putting 1024 bytes on the stack:

    unsigned int chip[256];

...and it's also undesirable to have a hard limit on the number of
CPUs here.

Fix both problems by dynamically allocating based on num_possible_cpus,
as recommended by Michael Ellerman.

Fixes: 053819e ("cpufreq: powernv: Handle throttling due to Pmax capping at chip level")
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Cc: 4.10+ <stable@vger.kernel.org> # 4.10+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/powernv-cpufreq.c

@@ -1041,9 +1041,14 @@ static struct cpufreq_driver powernv_cpufreq_driver = {
 
 static int init_chip_info(void)
 {
-	unsigned int chip[256];
+	unsigned int *chip;
 	unsigned int cpu, i;
 	unsigned int prev_chip_id = UINT_MAX;
+	int ret = 0;
+
+	chip = kcalloc(num_possible_cpus(), sizeof(*chip), GFP_KERNEL);
+	if (!chip)
+		return -ENOMEM;
 
 	for_each_possible_cpu(cpu) {
 		unsigned int id = cpu_to_chip_id(cpu);
@@ -1055,8 +1060,10 @@ static int init_chip_info(void)
 	}
 
 	chips = kcalloc(nr_chips, sizeof(struct chip), GFP_KERNEL);
-	if (!chips)
-		return -ENOMEM;
+	if (!chips) {
+		ret = -ENOMEM;
+		goto free_and_return;
+	}
 
 	for (i = 0; i < nr_chips; i++) {
 		chips[i].id = chip[i];
@@ -1066,7 +1073,9 @@ static int init_chip_info(void)
 			per_cpu(chip_info, cpu) =  &chips[i];
 	}
 
-	return 0;
+free_and_return:
+	kfree(chip);
+	return ret;
 }
 
 static inline void clean_chip_info(void)