drm/amdkfd: Remove kfd_process_hw_exception worker

With GPU reset-domain worker implemented, KFD hw_exception worker is not
needed any more, just call amdgpu_amdkfd_gpu_reset directly from
kfd_hws_hang.

Suggested-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>