Doc: driver-api: ipmi: Add description of alerts_broken module param

Add description about alerts_broken module parameter of ipmi_ssif driver
which skips enabling SMBus alert during setup.

Signed-off-by: Misono Tomohiro <misono.tomohiro@jp.fujitsu.com>
Message-Id: <20200624065405.17653-3-misono.tomohiro@jp.fujitsu.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>