Under bare metal, there is no more else to take
care of the GPU register access through MMIO.
Under Virtualization, to access GPU register is
implemented through KIQ during run-time due to
world-switch.

Therefore, under SR-IOV user can only access
debugfs to r/w GPU registers when meets all
three conditions below.
- amdgpu_gpu_recovery=0
- TDR happened
- in_gpu_reset=0

v2: merge amdgpu_virt_can_access_debugfs() into
    amdgpu_virt_enable_access_debugfs()

v3: drop ret variable in amdgpu_virt_enable_access_debugfs()
    and directly return result
Signed-off-by: Yintian Tao <yttao@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>