Add basic thermal driver for bcm2835 SoC.

This driver currently make sure that tsense HW block is set up
correctly.
Tested-by: NRafał Miłecki <rafal@milecki.pl>
Signed-off-by: NMartin Sperl <kernel@martin.sperl.org>
Signed-off-by: NStefan Wahren <stefan.wahren@i2se.com>
Acked-by: NEric Anholt <eric@anholt.net>
Acked-by: NEduardo Valentin <edubezval@gmail.com>
Signed-off-by: NEduardo Valentin <edubezval@gmail.com>