ARM: dts: aspeed: mtjade,mtmitchell: Add BMC SSIF nodes

Add BMC SSIF node to support IPMI in-band communication.

Signed-off-by: Quan Nguyen <quan@os.amperecomputing.com>
Link: https://lore.kernel.org/r/20221024081115.3320584-1-quan@os.amperecomputing.com


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