ipmi: add SET_SENSOR_READING command

ipmi: add SET_SENSOR_READING command

SET_SENSOR_READING is a complex IPMI command (see IPMI spec 35.17)
which enables the host software to set the reading value and the event
status of sensors supporting it.

Below is a proposal for all the operations (reading, assert, deassert,
event data) with the following limitations :

 - No event are generated for threshold-based sensors.
 - The case in which the BMC needs to generate its own events is not
   supported.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Corey Minyard <cminyard@mvista.com>
Message-Id: <20191118092429.16149-1-clg@kaod.org>
[Moved the break statement for case SENSOR_GEN_EVENT_DATA above the
 closing brace to keep the indention consistent.]
Signed-off-by: Corey Minyard <cminyard@mvista.com>