ARM: dts: aspeed: Add KCS support for LPC BMC

This adds the description of the four Keyboard Controller Style (KCS)
IPMI communication channels present in the ASPEED BMC. They are disabled
by default.

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