drm/tests: add missing MODULE_DESCRIPTION() macros

drm/tests: add missing MODULE_DESCRIPTION() macros

make allmodconfig && make W=1 C=1 reports:
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/tests/drm_kunit_helpers.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/tests/drm_buddy_test.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/tests/drm_cmdline_parser_test.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/tests/drm_connector_test.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/tests/drm_damage_helper_test.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/tests/drm_dp_mst_helper_test.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/tests/drm_exec_test.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/tests/drm_format_test.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/tests/drm_framebuffer_test.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/tests/drm_gem_shmem_test.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/tests/drm_managed_test.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/tests/drm_mm_test.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/tests/drm_modes_test.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/tests/drm_plane_helper_test.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/tests/drm_probe_helper_test.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/tests/drm_rect_test.o

Add the missing invocations of the MODULE_DESCRIPTION() macro.

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240606-md-drivers-gpu-drm-tests-v1-1-228ca6213969@quicinc.com