cpufreq: scpi: Add thermal dependency

A built-in scpi cpufreq driver cannot link against a modular
thermal framework:

drivers/cpufreq/scpi-cpufreq.o: In function `scpi_cpufreq_ready':
scpi-cpufreq.c:(.text+0x4c): undefined reference to `of_cpufreq_cooling_register'
drivers/cpufreq/scpi-cpufreq.o: In function `scpi_cpufreq_exit':
scpi-cpufreq.c:(.text+0x9c): undefined reference to `cpufreq_cooling_unregister'

This adds a Kconfig dependency that makes sure this configuration
is not possible, while allowing all configurations that can work.
Note that disabling CPU_THERMAL means we don't care about the
THERMAL dependency.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Sudeep Holla <sudeep.holla@arm.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>