ipmi: kcs_bmc_aspeed: Implement KCS SerIRQ configuration

Apply the SerIRQ ID and level/sense behaviours from the devicetree if
provided.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Message-Id: <20210608104757.582199-15-andrew@aj.id.au>
Signed-off-by: Corey Minyard <cminyard@mvista.com>