utils/genrandconfig: fix fallout of dropping toolchain CSV

Commit 2f260084d577 (utils/genrandconfig: remove support for toolchain
CSV) kept the --no-toolchains-csv option, but in the rework forgot to
keep it as a bool, while argparse default is to expect a string.

Rather than re-introduce the action="store_true" which implies the
argument is a bool, explicit make it a bool.

Fixes: 2f260084d5771728f3340ff6a86a23391133a635

Reported-by: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

utils/genrandconfig

@@ -611,7 +611,7 @@ if __name__ == '__main__':
                         help="Buildroot directory (relative to current directory)",
                         type=str, default='.')
     parser.add_argument("--toolchains-csv", help="Legacy, unused", type=str)
-    parser.add_argument("--no-toolchains-csv", help="Legacy, unused")
+    parser.add_argument("--no-toolchains-csv", help="Legacy, unused", type=bool)
 
     args = parser.parse_args()