drm/xe: Group normal kunit tests in a single module

Creating one module for each compilation unit to be tested seems
excessive as the number of tests increase. Group them all in a single
kunit test module called xe_test.ko.

The tests requiring the physical device, aka "live" tests, are still
kept in separate modules since they are normally triggered via igt,
and not via kunit.py. After igt is converted, those can be merged in
a single module as well.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Acked-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231122203147.988021-2-lucas.demarchi@intel.com