thermal: armada: remove sensors validity from the IP initialization

When using new bindings with multiple sensors, sensor validity is
checked twice because sensor selection also checks for the validity.

Remove the redundant call from the IP initialization helper and move it
to the legacy probe section where it is still needed.

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