misc-habanalabs-fixes-2019-05-24

- Halt debug engines when user process closes the FD. We can't allow the
  device to issue transactions for a user which doesn't exists anymore.

- Fix various security holes in debugfs API.

- Add a new opcode to the DEBUG IOCTL API. The opcode is designed
  for setting the device into and out of debug mode. Although not a fix
  per-se, because this is a new IOCTL which is upstreamed in kernel 5.2, I
  think this is justified at this point because we won't be able to change
  the API later.

- Fix a bug where the code used an uninitialized mutex