tools: Add script to check usage of banned functions

This script can be run locally via ./tools/check_api.py. When forbidden
functions are found, filename and line number for each match are printed on the
error output before the function name.

Change-Id: I1668e9e4f2a57d37b62ee984086edff9651132ec
Signed-off-by: Raphael Gault <raphael.gault@arm.com>