tmc: Add support for virtual enable pins

Add support for enabling the stepper via the communication channel.
This improves support for boards with a shared enable line.

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

klippy/extras/tmc2209.py

@@ -59,6 +59,8 @@ class TMC2209:
         self.fields = tmc.FieldHelper(Fields, tmc2208.SignedFields,
                                       FieldFormatters)
         self.mcu_tmc = tmc_uart.MCU_TMC_uart(config, Registers, self.fields)
+        # Allow virtual pins to be created
+        tmc.TMCVirtualPinHelper(config, self.mcu_tmc)
         # Register commands
         cmdhelper = tmc.TMCCommandHelper(config, self.mcu_tmc)
         cmdhelper.setup_register_dump(ReadRegisters)