drm/amdgpu: add amdgpu.ptl module parameter for PTL control

drm/amdgpu: add amdgpu.ptl module parameter for PTL control

Add a new kernel module parameter 'amdgpu.ptl' to allow
users to enable or disable PTL feature at driver loading time.

Parameter values:
  *) 0 or -1: disable PTL (default)
  *) 1: enable PTL
  *) 2: permanently disable PTL

Signed-off-by: Perry Yuan <perry.yuan@amd.com>
Reviewed-by: Yifan Zhang <yifan1.zhang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>