serial: 8250: add LPC18xx/43xx UART driver

Serial port driver for the 8250-based UART found on LPC18xx/43xx
devices. The UART is 16550A compatible with additional features
like RS485 support, synchronous mode, IrDA, and DMA.

For now only basic UART and RS485 operation is supported.

Signed-off-by: Joachim Eastwood <manabian@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>