ipmi: convert locked counters to atomics

Atomics are a lot more efficient and neat than using a lock.
Signed-off-by: NKonstantin Baydarov <kbaidarov@ru.mvista.com>
Signed-off-by: NCorey Minyard <cminyard@mvista.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>