thermal: db8500: Finalize device tree conversion

At some point there was an attempt to convert the DB8500
thermal sensor to device tree: a probe path was added
and the device tree was augmented for the Snowball board.
The switchover was never completed: instead the thermal
devices came from from the PRCMU MFD device and the probe
on the Snowball was confused as another set of configuration
appeared from the device tree.

Move over to a device-tree only approach, as we fixed up
the device trees.

Cc: Vincent Guittot <vincent.guittot@linaro.org>
Acked-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>