thermal/drivers/hisi: Factor out the probe functions

The hi6220 and the hi3660 probe functions are doing almost the same
operations, they can share 90% of their code.

Factor out the probe functions by moving the common code in the common
probe function.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>