thermal/drivers/exynos: Split initialization of TMU and the thermal zone

This will be needed in the future, as the thermal zone subsystem might
call our callbacks right after devm_thermal_of_zone_register. Currently
we just make get_temp return EAGAIN in such case, but this will not be
possible with state-modifying callbacks, for instance set_trips.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Mateusz Majewski <m.majewski2@samsung.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20231201095625.301884-8-m.majewski2@samsung.com