dt-bindings: ipmi: aspeed: Introduce a v2 binding for KCS

The v2 binding utilises reg and renames some of the v1 properties.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Message-Id: <8aec8994bbe1186d257b0a712e13cf914c5ebe35.1576462051.git-series.andrew@aj.id.au>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Corey Minyard <cminyard@mvista.com>