hw/misc: Model KCS devices in the Aspeed LPC controller

hw/misc: Model KCS devices in the Aspeed LPC controller

Keyboard-Controller-Style devices for IPMI purposes are exposed via LPC
IO cycles from the BMC to the host.

Expose support on the BMC side by implementing the usual MMIO
behaviours, and expose the ability to inspect the KCS registers in
"host" style by accessing QOM properties associated with each register.

The model caters to the IRQ style of both the AST2600 and the earlier
SoCs (AST2400 and AST2500). The AST2600 allocates an IRQ for each LPC
sub-device, while there is a single IRQ shared across all subdevices on
the AST2400 and AST2500.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20210302014317.915120-6-andrew@aj.id.au>
Signed-off-by: Cédric Le Goater <clg@kaod.org>