ARM: dts: aspeed: Add Microsoft Olympus BMC

Olympus is a Microsoft OCP platform equipped with Aspeed 1250 or
2400 BMC SoC.

Signed-off-by: Hongwei Zhang <hongweiz@ami.com>
Reviewed-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Joel Stanley <joel@jms.id.au>