atmel_mxt - Issue RESET in Acer C720P touch-screen driver

atmel_mxt - Issue RESET in Acer C720P touch-screen driver

* Sometimes the hardware appears to lose it, resulting in non-deterministic
  reporting of phantom fixed coordinate presses and movement which messes
  up X's pointer position.  This problem can survive a reboot.

* Issue a RESET command to the chipset on attach.  This will clear up
  any issues that would otherwise survive reboot.

* Add a sysctl, setting debug.atmel_mxt_reset=1 will cause the chipset
  to be reset.  If the chipset goes nuts on a live system, issuing this
  sysctl should clear it up.

  Detection of the situation not yet in place, so for now this sysctl must
  be issued manually if the problem occurs.