Check for the sispm dependency

From the commit that added it:

    Using it requires the following extra dependencies:
    $ apt-get install python3-usb
    $ pip3 install pysispm

Change-Id: Id347604f47ac5243b7eae12b9bdf675f2379f4c6

check_dependencies.py

@@ -24,5 +24,6 @@ import traceback
 import yaml
 import pydbus
 import sqlite3
+import sispm
 
 print('dependencies ok')