USB HID keyboard demo with lower power on suspend

Demonstrates how to configure the USB device controller as a HID keyboard class
device. If USB is suspended LP1 is entered and can wakeup on on VBUS. This demo
requires a board modification of connecting D+ to a GPIO. See R69 and R70 on the
schematic.

Example functionality:
  1. LED0 will illuminate once enumeration and configuration is complete.
  2. Open a text editor on the PC host and place cursor in edit box.
  3. Pressing pushbutton SW1 will cause a message to be typed in on a virtual
     keyboard one character at a time.
  4. To suspend USB put PC host in sleep mode. Observe lower current on VDD12.
  5. Wake up host PC and observe current on VDD12 is higher and the program
     resumes.

Jumper Configuration:
  No jumper configuration is required for the Demo program.
