serial: 8250_fintek: Add F81866 Support

Fintek F81866 is a LPC to 6 UARTs SuperIO. It has fully functional UARTs
likes F81216H. It's also need check the IRQ mode with system assigned,
but the configuration is not the same with F81216 series.

F81866 IRQ Mode setting:
	0xf0
		Bit1: IRQ_MODE0
		Bit0: Share mode (always on)
	0xf6
		Bit3: IRQ_MODE1

	Level/Low: IRQ_MODE0:0, IRQ_MODE1:0
	Edge/High: IRQ_MODE0:1, IRQ_MODE1:0

The following list is brief descriptions of F81866:

F81866 (1010)
	9Bit/High baud rate(not implements with mainline)
	RS485, 128Bytes FIFO (implemented)

Signed-off-by: Ji-Ze Hong (Peter Hong) <hpeter+linux_kernel@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>