tools/pyboard.py: Make --no-soft-reset consistent with other args.

This makes it work like --no-follow and --no-exclusive using a mutex group
and dest.  Although the current implementation with BooleanOptionAction is
neater it requires Python 3.9, so don't use this feature.
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

tools/pyboard.py

@@ -655,11 +655,17 @@ def main():
         type=int,
         help="seconds to wait for USB connected board to become available",
     )
-    cmd_parser.add_argument(
+    group = cmd_parser.add_mutually_exclusive_group()
+    group.add_argument(
         "--soft-reset",
         default=True,
-        action=argparse.BooleanOptionalAction,
-        help="Whether to perform a soft reset when connecting to the board.",
+        action="store_true",
+        help="Whether to perform a soft reset when connecting to the board [default]",
+    )
+    group.add_argument(
+        "--no-soft-reset",
+        action="store_false",
+        dest="soft_reset",
     )
     group = cmd_parser.add_mutually_exclusive_group()
     group.add_argument(