klippy: Introduce load_config_prefix() for modules that take parameters

Use both load_config() and load_config_prefix() functions when
dynamically loading a module from the extras directory - if the config
section name has parameters in it then use load_config_prefix().

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/extras/multi_pin.py

@@ -50,5 +50,5 @@ class PrinterMultiPin:
         for mcu_pin in self.mcu_pins:
             mcu_pin.set_pwm(print_time, value)
 
-def load_config(config):
+def load_config_prefix(config):
     return PrinterMultiPin(config)