Merge tag 'tags/bcm2835-drivers-next-2018-11-27' into drivers/next

This pull request adds SPDX to BCM2835 drivers, and fixes some bugs in
the firmware driver (silently hanging if the VPU doesn't respond to a
mailbox transaction, and undersized buffers in the firmware property
transactions for tags that aren't used yet in the upstream).

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>