IPMI: Detect register spacing on PCI interfaces

The IPMI spec defines a way to detect register spacing for PCI interfaces,
so implement it.

Signed-off-by: Steven Hsieh <sshsieh@broadcom.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>