The Altera 16550 soft IP UART requires 2 additional registers for
TX FIFO threshold support. These 2 registers enable the TX FIFO
Low Watermark and set the TX FIFO Low Watermark.
Set the TX FIFO threshold to the FIFO size - tx_loadsz.
Signed-off-by: NThor Thayer <tthayer@opensource.altera.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>