The function is now used only in qemu_process.c so move it there and
name it 'qemuProcessPrepareQEMUCaps' which is more appropriate to what
it's doing.

The reworded comment now mentions that it will also post-process the
caps for VM startup.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>