Disable coverage collection for testbench related verilog files (#1204)

vsrc/SimDTM.v

@@ -1,4 +1,5 @@
 // See LICENSE.SiFive for license details.
+//VCS coverage exclude_file
 
 import "DPI-C" function int debug_tick
 (

vsrc/SimJTAG.v

@@ -1,5 +1,5 @@
 // See LICENSE.SiFive for license details.
-
+//VCS coverage exclude_file
 import "DPI-C" function int jtag_tick
 (
  output bit jtag_TCK,

vsrc/TestDriver.v

@@ -1,5 +1,5 @@
 // See LICENSE.SiFive for license details.
-
+//VCS coverage exclude_file
 `ifndef RESET_DELAY
  `define RESET_DELAY 777.7
 `endif

vsrc/jtag_vpi.v

@@ -31,7 +31,7 @@
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  * POSSIBILITY OF SUCH DAMAGE.
  */
-
+//VCS coverage exclude_file
 `define CMD_RESET		0
 `define CMD_TMS_SEQ		1
 `define CMD_SCAN_CHAIN		2

vsrc/plusarg_reader.v

@@ -1,5 +1,7 @@
 // See LICENSE.SiFive for license details.
 
+//VCS coverage exclude_file
+
 // No default parameter values are intended, nor does IEEE 1800-2012 require them (clause A.2.4 param_assignment),
 // but Incisive demands them. These default values should never be used.
 module plusarg_reader #(parameter FORMAT="borked=%d", DEFAULT=0) (