thermal: bcm2835: add thermal driver for bcm2835 SoC

Add basic thermal driver for bcm2835 SoC.

This driver currently make sure that tsense HW block is set up
correctly.

Tested-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Martin Sperl <kernel@martin.sperl.org>
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Acked-by: Eric Anholt <eric@anholt.net>
Acked-by: Eduardo Valentin <edubezval@gmail.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>