We don't want a separate module for vb2-trace.
That fixes this warning:
WARNING: modpost: missing MODULE_LICENSE() in drivers/media/common/videobuf2/vb2-trace.o
When building as module.
While here, add a SPDX header.
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>