ARM: dts: aspeed: Adding Facebook TiogaPass BMC

Initial introduction of Facebook TiogaPass family equipped with
Aspeed 2500 BMC SoC. TiogaPass is a x86 server development kit
with a ASPEED ast2500 BMC manufactured by Facebook.

Specifically, This adds the TiogaPass platform device tree file
including the flash layout used by the TiogaPass BMC machines.

Signed-off-by: Vijay Khemka <vijaykhemka@fb.com>
Signed-off-by: Joel Stanley <joel@jms.id.au>