cros_bundle_firmware: Tidy up servo messages

When using '--servo none' we should not say that we are using servo to
reset the board.

BUG=chromium:216858
TEST=manual
Try on link with '--servo none' and check that the reset message no longer
appears, and link is not reset. Try with '--servo 7777' and see that it
does print the message and reset.

Also try the same with snow.

Change-Id: I9d28ed69e6cbe5f5bf169a0921b3f45d6277c1f6
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/49402
diff --git a/host/lib/write_firmware.py b/host/lib/write_firmware.py
index 70fec94..28e6a91 100644
--- a/host/lib/write_firmware.py
+++ b/host/lib/write_firmware.py
@@ -550,8 +550,9 @@
     if preserved_dut_hub_sel != required_dut_hub_sel:
       # Need to set it to get the port properly powered up.
       args += ['dut_hub_sel:%s' % required_dut_hub_sel]
-    self._out.Progress('Reseting board via servo')
-    self.DutControl(args)
+    if self._servo_port is not None:
+      self._out.Progress('Reseting board via servo')
+      self.DutControl(args)
 
     # If we have a kernel to write, create a new image with that added.
     if kernel:
@@ -775,10 +776,11 @@
     self._out.Progress('Writing image to em100')
     self._tools.Run('em100', args, sudo=True)
 
-    self._out.Progress('Resetting board')
-    args = ['cold_reset:on', 'sleep:.2', 'cold_reset:off', 'sleep:.5']
-    args.extend(['pwr_button:press', 'sleep:.2', 'pwr_button:release'])
-    self.DutControl(args)
+    if self._servo_port is not None:
+      self._out.Progress('Resetting board via servo')
+      args = ['cold_reset:on', 'sleep:.2', 'cold_reset:off', 'sleep:.5']
+      args.extend(['pwr_button:press', 'sleep:.2', 'pwr_button:release'])
+      self.DutControl(args)
 
 
 def DoWriteFirmware(output, tools, fdt, flasher, file_list, image_fname,