drm/amdgpu: route ioctls on primary node of XCPs to primary device

drm/amdgpu: route ioctls on primary node of XCPs to primary device

During XCP init, unlike the primary device, there is no amdgpu_device
attached to each XCP's drm_device

In case that user trying to open/close the primary node of XCP drm_device
this rerouting is to solve the NULL pointer issue causing by referring
to any member of the amdgpu_device

 BUG: unable to handle page fault for address: 0000000000020c80
 #PF: supervisor write access in kernel mode
 #PF: error_code(0x0002) - not-present page
 Oops: 0002 [#1] PREEMPT SMP NOPTI
 Call Trace:
  <TASK>
  lock_timer_base+0x6b/0x90
  try_to_del_timer_sync+0x2b/0x80
  del_timer_sync+0x29/0x40
  flush_delayed_work+0x1c/0x50
  amdgpu_driver_open_kms+0x2c/0x280 [amdgpu]
  drm_file_alloc+0x1b3/0x260 [drm]
  drm_open+0xaa/0x280 [drm]
  drm_stub_open+0xa2/0x120 [drm]
  chrdev_open+0xa6/0x1c0

Signed-off-by: Shiwu Zhang <shiwu.zhang@amd.com>
Reviewed-by: Le Ma <le.ma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>