Convert WeDo driver to new lego bus

* The WeDo hub itself is now a lego-sensor. The status and voltage attributes
  are converted to values and the other attributes are converted to commands.
  Reset is removed because it seems to lock up the WeDo hub. High Power is
  removed and is instead automatically detected based on the current availible
  reported by the USB port that the WeDo hub is connected to.
* The WeDo ports are now lego-port devices.
* Sensor, motor and led devices remain the same.
* Fixed sleeping (registering/unregistering sensor/motor/led devices) in
  interrupt context.
* Also includes some code cleanup.
Give LEGO-driver-specific uevent properties a namespace and change name attributes to device_name.

ev3dev/ev3dev#223
Fix compiler warning about const.
Fix crash in UART sensor line discipline.

We are no longer using platform_data for the port device, which caused the
crash. Also, the #ifdefs are no longer necessary because we are not using
platform specific info anymore.
More versitle custom scaling in lego-sensor class.

The existing method of scaling by calling a callback function each time a value
was updated resulted in much duplication of code. It also did not allow for the
scaled value to be larger than the raw value data type.

Scaling is now only performed when reading the value* attributes, which will
improve performace as well.

Had to remove debounce from wedo tilt sensor. A more generic debounce that can
be used by all sensors needs to be implemented instead. This should be done in
conjunction with adding sysfs_notify calls.

Also added PROXY mode to wedo motion sensor.