ARM: dts: aspeed: Add Inspur fp5280g2 BMC machine

The fp5280g2 is an OpenPower server platform with an ASPEED AST2500 BMC.

Signed-off-by: John Wang <wangzqbj@inspur.com>
Reviewed-by: Lei YU <mine260309@gmail.com>
Reviewed-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Joel Stanley <joel@jms.id.au>