kunit: Allow kunit test modules to use test filtering

External tools, e.g., Intel GPU tools (IGT), support execution of
individual selftests provided by kernel modules.  That could be also
applicable to kunit test modules if they provided test filtering.  But
test filtering is now possible only when kunit code is built into the
kernel.  Moreover, a filter can be specified only at boot time, then
reboot is required each time a different filter is needed.

Build the test filtering code also when kunit is configured as a module,
expose test filtering functions to other kunit source files, and use them
in kunit module notifier callback functions.  Userspace can then reload
the kunit module with a value of the filter_glob parameter tuned to a
specific kunit test module every time it wants to limit the scope of tests
executed on that module load.  Make the kunit.filter* parameters visible
in sysfs for user convenience.

v5: Refresh on tpp of attributes filtering fix
v4: Refresh on top of newly applied attributes patches and changes
    introdced by new versions of other patches submitted in series with
    this one.
v3: Fix CONFIG_GLOB, required by filtering functions, not selected when
    building as a module (lkp@intel.com).
v2: Fix new name of a structure moved to kunit namespace not updated
    across all uses (lkp@intel.com).

Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>