This adds driver for the UART controller on Atmel SAM3X8E.
This UART controller only has two wires for RX and TX, and
does not have flow control (e.g. CTS, RTS) or FIFO.
Currently, the driver does not support any interrupt driven
operations.
Change-Id: I63720bccfb70a89888353b8ee3dfc4b80793dc01
Signed-off-by: Daniel Leung <daniel.leung@intel.com>