board_inspector: add a missing module import

This patch adds the import of the `sys` module in platformbase.py which
uses `sys.exit` to terminate the board inspector upon fatal errors.

Tracked-On: #6689
Signed-off-by: Junjie Mao <junjie.mao@intel.com>

misc/config_tools/board_inspector/cpuparser/platformbase.py

@@ -6,6 +6,7 @@
 """Base classes and infrastructure for CPUID and MSR decoding"""
 
 from __future__ import print_function
+import sys
 import subprocess # nosec
 import re
 import functools