Added support for the LPC11U68 and LPC1549 LPCXpresso Boards

* Added support for the LPC11U68 target MCU with LPC4322 as interface MCU
* Added support for the LPC1549 target MCU with LPC4322 as interface MCU
* Added weak board_init() function (with default empty implementation) to allow initialization before the main task is started
* Changed the post flashing procedure to do a USB media eject/insert instead of restarting the entire USB stack. This means that the virtual COM port is not disconnected every time a new image is flashed - allowing a PC program to stay connected.
* Increased stack size of the TIMER_TASK_30 as it would cause an error when the OS stack check code was enabled
*