Document RIFSC (RIF security controller). RIFSC is a firewall controller
composed of different kinds of hardware resources.
Signed-off-by: Gatien Chevallier <gatien.chevallier@foss.st.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>