thermal: armada: add a function that sanitizes the thermal zone name

Thermal zone names must follow certain rules imposed by the framework.
They are limited in length and shall not have any hyphen '-'.

This is done in a separate function for future use in another location.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>