vts_mt: add the virtual multitouch touchscreen type A or B

Supports:
- x, y coordinates
- pressure
- distance

Calibration:
- width
- height
- max pressure
- max simultaneous fingers
- type

Event format:
id,x,y,z

where:
- id is the toucvh event id (used for type B tracking)
- down is the up/down info
- x, y coordinates
- z pressure or distance info (pressure if positive, distance if negative, touch release if 0)