ARM: dts: aspeed: p10bmc: Enable KCS channel 2

Rainier uses KCS channel 2 as the source for the debug-trigger
application outlined at [1] and implemented at [2].

[1] https://github.com/openbmc/docs/blob/master/designs/bmc-service-failure-debug-and-recovery.md
[2] https://github.com/openbmc/debug-trigger



Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Link: https://lore.kernel.org/r/20210623033854.587464-8-andrew@aj.id.au


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