ARM: dts: aspeed: Add ASRock E3C246D4I BMC

This is a relatively low-cost AST2500-based Xeon E-2100/E-2200 series
mini-ITX board that we hope can provide a decent platform for OpenBMC
development.

This initial device-tree provides the necessary configuration for
basic BMC functionality such as host power control, serial console and
KVM support, and POST code snooping.

Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20210401044232.9637-1-zev@bewilderbeest.net
Signed-off-by: Joel Stanley <joel@jms.id.au>