thermal: armada: remove misleading comments

On older versions of this thermal IP, TSEN referred as the internal
sensor in the thermal IP while EXT_TSEN referred as sensors outside of
this IP, ie in the CPUs most of the time. The bit names in the
specifications do not follow this rule anymore, so remove these comments
that are misleading.

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