Make struct proc_ipmi_root static.

Besides this, tremove removes an unused #ifdef CONFIG_PROC_FS from
include/linux/ipmi.h.
Acked-by: NCorey Minyard <minyard@acm.org>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>