ipmi: Remove the now unnecessary message queue

A message queue was added to the message handler, so the SMI
interfaces only need to handle one message at a time.  Pull out
the message queue.  This also leads to some significant
simplification in the shutdown of an interface, since the
message handler now does a lot of the cleanup.

Signed-off-by: Corey Minyard <cminyard@mvista.com>

diff --cc drivers/char/ipmi/ipmi_si_intf.c
Simple merge