drm/tests: Build KMS helpers when DRM_KUNIT_TEST_HELPERS is enabled

Commit 66671944 ("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: 66671944 ("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.comSigned-off-by: Maxime Ripard <mripard@kernel.org>

drivers/gpu/drm/Kconfig

@@ -68,6 +68,7 @@ config DRM_USE_DYNAMIC_DEBUG
 config DRM_KUNIT_TEST_HELPERS
 	tristate
 	depends on DRM && KUNIT
+	select DRM_KMS_HELPER
 	help
 	  KUnit Helpers for KMS drivers.
 
@@ -80,7 +81,6 @@ config DRM_KUNIT_TEST
 	select DRM_EXEC
 	select DRM_EXPORT_FOR_TESTS if m
 	select DRM_GEM_SHMEM_HELPER
-	select DRM_KMS_HELPER
 	select DRM_KUNIT_TEST_HELPERS
 	select DRM_LIB_RANDOM
 	select PRIME_NUMBERS