ARM: dts: aspeed: Add Supermicro x11spi BMC machine

The x11spi is a server platform with an ASPEED AST2500 BMC.

Signed-off-by: Ryan Sie <ryans@supermicro.com.tw>
Link: https://lore.kernel.org/r/20201221134315.5544-1-RyanS@supermicro.com.tw


Signed-off-by: Joel Stanley <joel@jms.id.au>