drm/tests: Build KMS helpers when DRM_KUNIT_TEST_HELPERS is enabled

drm/tests: Build KMS helpers when DRM_KUNIT_TEST_HELPERS is enabled

Commit 66671944e176 ("drm/tests: helpers: Add atomic helpers")
introduced a dependency on CRTC helpers in KUnit test helpers.
Select the former when building KUnit test helpers to avoid
linker errors.

Fixes: 66671944e176 ("drm/tests: helpers: Add atomic helpers")
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Maíra Canal <mcanal@igalia.com>
Signed-off-by: Karolina Stolarek <karolina.stolarek@intel.com>
Link: https://lore.kernel.org/r/20240313142142.1318718-1-karolina.stolarek@intel.com
Signed-off-by: Maxime Ripard <mripard@kernel.org>