8250_pci: add support for National Instruments 843x RS232 devices

This implements basic support for all 843x RS232 devices, but does not
add DMA support.  This means that sustained data transfers at high baud
rates may not be possible on multiple ports simultaneously.

Signed-off-by: Shawn Bohrer <shawn.bohrer@ni.com>
Signed-off-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>