ARM: dts: aspeed: Add Inspur on5263m5 BMC

The Inspur on5263m5 is an Intel Xeon OCP server that uses the ASPEED
AST2500 BMC.

Signed-off-by: John Wang <wangzqbj@inspur.com>
Reviewed-by: Andrew Jeffery <andrew@aj.id.au>
[joel: Rework commit message]
Signed-off-by: Joel Stanley <joel@jms.id.au>