MAINTAINERS: update Broadcom ARM tree location and add an SoC family

The Broadcom ARM tree location has changed names to reflect other SoC
families that are queued here. Also add the 216xx family as maintained.

Signed-off-by: Matt Porter <mporter@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>

diff --cc MAINTAINERS
Simple merge