thermal: armada: Add generic infrastructure to handle the sensor

In order to support similar SoC where the sensor value and valid
bit can have different shifts and/or mask, we add such fields to the
per-variant structure, instead of having the values hardcoded.

Acked-by: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>