U4RXREG is the RX buffer for UART4. U4RXR is the register for
controlling the input pin for UART4.
Signed-off-by: Francois Berder <francois.berder@imgtec.com>
Since the UART module takes control of RX and TX pins, there
is no need to configure the pins.
Signed-off-by: Francois Berder <francois.berder@imgtec.com>