tools: exclude test mock directories

Upcoming unit testing patches autogenerate mock
files which shouldn't be subject to the usual code style
checks. Module-specific mocks will be held in "module/*/test/mocks",
so an expanded glob is used to exclude all of these
directories.

Signed-off-by: Brett Warren <brett.warren@arm.com>
Change-Id: I840ebce8d14344d625476cde9fd1fd71501af475