cpufreq: scmi: add thermal dependency

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

drivers/cpufreq/scmi-cpufreq.o: In function `scmi_cpufreq_ready':
scmi-cpufreq.c:(.text+0x40): undefined reference to `of_cpufreq_cooling_register'
drivers/cpufreq/scmi-cpufreq.o: In function `scmi_cpufreq_exit':
scmi-cpufreq.c:(.text+0x88): 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.

Acked-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>