thermal: cpu_cooling: Require thermal core to be compiled in

thermal: cpu_cooling: Require thermal core to be compiled in

The CPU cooling driver (cpu_cooling.c) allows the platform's cpufreq
driver to register as a cooling device and cool down the platform by
throttling the CPU frequency. In order to be able to auto-register a
cpufreq driver as a cooling device from the cpufreq core, we need access
to code inside cpu_cooling.c which, in turn, accesses code inside
thermal core.

CPU_FREQ is a bool while THERMAL is tristate.  In some configurations
(e.g. allmodconfig), CONFIG_THERMAL ends up as a module while
CONFIG_CPU_FREQ is compiled in. This leads to following error:

drivers/cpufreq/cpufreq.o: In function `cpufreq_offline':
cpufreq.c:(.text+0x407c): undefined reference to `cpufreq_cooling_unregister'
drivers/cpufreq/cpufreq.o: In function `cpufreq_online':
cpufreq.c:(.text+0x70c0): undefined reference to `of_cpufreq_cooling_register'

Given that platforms using CPU_THERMAL usually want it compiled-in so it
is available early in boot, make CPU_THERMAL depend on THERMAL being
compiled-in instead of allowing it to be a module.

As a result of this change, get rid of the ugly (!CPU_THERMAL ||
THERMAL) dependency in all cpufreq drivers using CPU_THERMAL.

Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>