ipmi_si: Only schedule continuously in the thread in maintenance mode

[ Upstream commit 340ff31ab00bca5c15915e70ad9ada3030c98cf8 ]

ipmi_thread() uses back-to-back schedule() to poll for command
completion which, on some machines, can push up CPU consumption and
heavily tax the scheduler locks leading to noticeable overall
performance degradation.

This was originally added so firmware updates through IPMI would
complete in a timely manner.  But we can't kill the scheduler
locks for that one use case.

Instead, only run schedule() continuously in maintenance mode,
where firmware updates should run.

Signed-off-by: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>