thermal/drivers/Kconfig: Convert the CPU cooling device to a choice

The next changes will add a new way to cool down a CPU by injecting
idle cycles. With the current configuration, a CPU cooling device is
the cpufreq cooling device. As we want to add a new CPU cooling
device, let's convert the CPU cooling to a choice giving a list of CPU
cooling devices. At this point, there is obviously only one CPU
cooling device.

There is no functional changes.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Link: https://lore.kernel.org/r/20191204153930.9128-1-daniel.lezcano@linaro.org
diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
index 79b2786..62c1c83 100644
--- a/drivers/thermal/Kconfig
+++ b/drivers/thermal/Kconfig
@@ -151,16 +151,26 @@
 
 config CPU_THERMAL
 	bool "Generic cpu cooling support"
-	depends on CPU_FREQ
 	depends on THERMAL_OF
 	help
+	  Enable the CPU cooling features. If the system has no active
+	  cooling device available, this option allows to use the CPU
+	  as a cooling device.
+
+if CPU_THERMAL
+
+config CPU_FREQ_THERMAL
+	bool "CPU frequency cooling device"
+	depends on CPU_FREQ
+	default y
+	help
 	  This implements the generic cpu cooling mechanism through frequency
 	  reduction. An ACPI version of this already exists
 	  (drivers/acpi/processor_thermal.c).
 	  This will be useful for platforms using the generic thermal interface
 	  and not the ACPI interface.
 
-	  If you want this support, you should say Y here.
+endif
 
 config CLOCK_THERMAL
 	bool "Generic clock cooling support"