Support BMC IPMI heartbeat command
Support BMC IPMI heartbeat command

A few years ago, the OpenBMC code added support for a "heartbeat"
command to send to the host. This command is used after the BMC is reset
to check if the host is running. Support was never added to the host
side however so currently when the BMC sends this command, this appears
in the host console:
IPMI: unknown OEM SEL command ff received

There is no response needed by the host (other then the low level
acknowledge of the command which already occurs). This commit
handles the command so the error is no longer printed (does nothing with
the command though since no action is needed). Here's the tested output
of this patch in the host console (with debug enabled):
IPMI: BMC issued heartbeat command: 00

Signed-off-by: Andrew Geissler <f7919ac9f8ec0c3ffbc3f483da625c634fd31638@yahoo.com>

shenki/skiboot,open-power/skiboot,qemu/skiboot,legoater/skiboot,qemu/skiboot,open-power/skiboot,qemu/skiboot,shenki/skiboot,qemu/skiboot,open-power/skiboot,qemu/skiboot,open-power/skiboot,shenki/skiboot,legoater/skiboot,legoater/skiboot,shenki/skiboot,legoater/skiboot,legoater/skiboot,shenki/skiboot,open-power/skiboot