serial: rp2: New driver for Comtrol RocketPort 2 cards

This driver supports the RocketPort EXPRESS and RocketPort INFINITY
families of PCI/PCIe multiport serial adapters.  These adapters use a
"RocketPort 2" ASIC that is not compatible with the original RocketPort
driver (CONFIG_ROCKETPORT).

Tested with the RocketPort EXPRESS Octa DB9 and Quad DB9.  Also added an
old RocketPort 8J PCI card to the same system to verify that rocket.c and
rp2.c coexist peacefully.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>