configs: Add --wait-gdb option to fs.py

Change-Id: Ib3174927ccc65ce1ddce450ce6020f74ea60d366
Signed-off-by: Kai Ren <binarystar2006@outlook.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/48944
Reviewed-by: Kai Ren <binarystar.kai.ren@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

configs/common/Options.py

@@ -533,3 +533,7 @@ def addFSOptions(parser):
     parser.add_argument(
         "--command-line-file", action="store", default=None, type=str,
         help="File with a template for the kernel command line")
+
+    # Debug option
+    parser.add_argument("--wait-gdb", default=False, action='store_true',
+                        help="Wait for remote GDB to connect.")