Added custom board option to STM Pins generation script

tools/targets/STM32_gen_PeripheralPins.py

@@ -1248,6 +1248,10 @@ specify the board file description in STM32CubeMX to use (use double quotes).
    Parameter can be a filter like L496 (only the first file found will be parsed).
 '''))
 
+group.add_argument("-c", "--custom", help=textwrap.dedent('''\
+specify a custom board .ioc file description to use (use double quotes).
+'''))
+
 args = parser.parse_args()
 
 if not(os.path.isdir(cubemxdir)):
@@ -1364,6 +1368,10 @@ if args.target:
     else:
         quit()
 
+# Parse the user's custom board .ioc file
+if args.custom:
+    parse_BoardFile(args.custom)
+
 for mcu_file in mcu_list:
     if args.mcu:
         TargetName = os.path.splitext(mcu_file)[0]