dt-bindings: reset: Document BCM7216 RESCAL reset controller

BCM7216 has a special purpose RESCAL reset controller for its SATA and
PCIe0/1 instances. This is a simple reset controller with #reset-cells
set to 0.

Signed-off-by: Jim Quinlan <jim2101024@gmail.com>
[florian: Convert to YAML binding]
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>