drm/amdgpu/userq: rework driver parameter

Replace disable_kq parameter with user_queue parameter.
The parameter has the following logic:
 -1 = auto (ASIC specific default)
  0 = user queues disabled
  1 = user queues enabled and kernel queues enabled (if supported)
  2 = user queues enabled and kernel queues disabled

The default behavior (-1) is currently the same as 0 for current
ASICs.  To enable user queues (in addition to kernel queues) set
user_queue=1. To enable user queues and disable kernel queues
(to make all resources available to user queues), set user_queue=2.

Reviewed-by: Sunil Khatri <sunil.khatri@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>