drivers: char: ipmi: ipmi_msghandler: Pass lockdep expression to RCU lists

intf->cmd_rcvrs is traversed with list_for_each_entry_rcu
outside an RCU read-side critical section but under the
protection of intf->cmd_rcvrs_mutex.

ipmi_interfaces is traversed using list_for_each_entry_rcu
outside an RCU read-side critical section but under the protection
of ipmi_interfaces_mutex.

Hence, add the corresponding lockdep expression to the list traversal
primitive to silence false-positive lockdep warnings, and
harden RCU lists.

Add macro for the corresponding lockdep expression to make the code
clean and concise.

Signed-off-by: Amol Grover <frextrite@gmail.com>
Message-Id: <20200117132521.31020-1-frextrite@gmail.com>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: John Garry <john.garry@huawei.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>