trace: Put all trace.o into libqemuutil.a

Currently all trace.o are linked into qemu-system, qemu-img,
qemu-nbd, qemu-io etc., even the corresponding components
are not included.
Put all trace.o into libqemuutil.a that the linker would only pull in .o
files containing symbols that are actually referenced by the
program.

Signed-off -by: Anthony Xu <anthony.xu@intel.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>