drm/xe: Fix modpost warning on kunit modules

When built with W=1, the following warnings show up on modpost:

	  MODPOST drivers/gpu/drm/xe/Module.symvers
	WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/xe/tests/xe_bo_test.o
	WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/xe/tests/xe_dma_buf_test.o
	WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/xe/tests/xe_migrate_test.o
	WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/xe/tests/xe_pci_test.o
	WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/xe/tests/xe_rtp_test.o
	WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/xe/tests/xe_wa_test.o

Add the module description for each of these to fix the warning.

Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://lore.kernel.org/r/20231120221904.695630-1-lucas.demarchi@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>