ipmi: add a KCS IPMI BMC driver

Provides a device driver for the KCS (Keyboard Controller Style)
IPMI interface which meets the requirement of the BMC (Baseboard
Management Controllers) side for handling the IPMI request from
host system software.

Signed-off-by: Haiyue Wang <haiyue.wang@linux.intel.com>
[Removed the selectability of IPMI_KCS_BMC, as it doesn't do much
 good to have it by itself.]
Signed-off-by: Corey Minyard <cminyard@mvista.com>