#644 PS2: Add support for combined keyboard+mouse usb devices

[citronalco]

I have a USB keyboard with an included touchpad connected to my slim Playstation2.
In ScummVM only the keys are working, the touchpad does not work.

In Blackrhino both keyboard and touchpad are working and showing up as follows:

Aug 25 17:37:37 blackrhino kernel: input0: USB HID v1.00 Keyboard [0c45:7403] on usb1:3.0
Aug 25 17:37:37 blackrhino kernel: input1: USB HID v1.00 Mouse [0c45:7403] on usb1:3.1

As many games require keyboard input and nearly all of them some kind of pointing device, it would be great if it would work in ScummVM