thermal: bcm2835: move to the broadcom subdirectory

We already have 2 Broadcom drivers and at least 1 more is coming. This
made us create broadcom subdirectory where bcm2835 should be moves now.

Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>