Verdi and VCS cosim

1. add fsdb functions into your testbench
  $fsdbDumpfile("test.fsdb");
  $fsdbDumpvars;
use `ifdef macros to optionally enable. Need to specify +define+DumpFSDB(`ifdef DumpFSDB) in your vcs command options

2. Find fsdb PLI lib files
  for vcs ${NOVAS_INST_DIR}/share/PLI/VCS/${PLATFORM}/pli.a(or novas.tab)
  also include the lib directory
  ${NOVAS_INST_DIR}/share/PLI/lib/${PLATFORM}
  better to specify the path for the LD_LIBRARY_PATH within your ~/.bashrc file

3. Specify the PLI archive files
  My method is copy the files(novas.tab and pli.a) into the working directory, and use the vcs command:
  vcs filename.v +v2k -P novas.tab pli.a(${abosulute_path/pli.a} if not copied)

4. ./simv to get the .fsdb file

5. use Verdi to check the .fsdb file
  command like, verdi -2001 -f vcs.args -ssf test.fsdb