cpufreq: Simplify core code related to boost support

Notice that the boost_supported field in struct cpufreq_driver is
redundant, because the driver's ->set_boost callback may be left
unset if "boost" is not supported.  Moreover, the only driver
populating the ->set_boost callback is acpi_cpufreq, so make it
avoid populating that callback if "boost" is not supported, rework
the core to check ->set_boost instead of boost_supported to
verify "boost" support and drop boost_supported which isn't
used any more.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
index 12da54a..51eef87 100644
--- a/drivers/cpufreq/acpi-cpufreq.c
+++ b/drivers/cpufreq/acpi-cpufreq.c
@@ -164,7 +164,7 @@
 	int ret;
 	unsigned int val = 0;
 
-	if (!acpi_cpufreq_driver.boost_supported)
+	if (!acpi_cpufreq_driver.set_boost)
 		return -EINVAL;
 
 	ret = kstrtouint(buf, 10, &val);
@@ -900,7 +900,6 @@
 	.resume		= acpi_cpufreq_resume,
 	.name		= "acpi-cpufreq",
 	.attr		= acpi_cpufreq_attr,
-	.set_boost      = set_boost,
 };
 
 static void __init acpi_cpufreq_boost_init(void)
@@ -911,7 +910,7 @@
 		if (!msrs)
 			return;
 
-		acpi_cpufreq_driver.boost_supported = true;
+		acpi_cpufreq_driver.set_boost = set_boost;
 		acpi_cpufreq_driver.boost_enabled = boost_state(0);
 
 		cpu_notifier_register_begin();