ipmi:si: Gracefully handle if the BMC is non-functional

If the BMC is not functional, the driver goes into an error state and
starts a 1 second timer.  When the timer times out, it will attempt a
simple message.  If the BMC interacts correctly, the driver will start
accepting messages again.  If not, it remains in error state.

If the driver goes into error state, all messages current and pending
will return with an error.

This should more gracefully handle when the BMC becomes non-operational,
as opposed to trying each messages individually and failing them.

Signed-off-by: Corey Minyard <corey@minyard.net>