Input: add new serio driver for Xilinx XPS PS2 IP

Added a new driver for Xilinx XPS PS2 IP. This driver is
a flat driver to better match the Linux driver pattern.

Signed-off-by: Sadanand <sadanan@xilinx.com>
Signed-off-by: John Linn <john.linn@xilinx.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>