drm/amdgpu: Fix resume failures when device is gone

Problem:
When device goes into suspend and unplugged during it
then all HW programming during resume fails leading
to a bad SW during pci remove handling which follows.
Because device is first resumed and only later removed
we cannot rely on drm_dev_enter/exit here.

Fix:
Use a flag we use for PCIe error recovery to avoid
accessing registres. This allows to successfully complete
pm resume sequence and finish pci remove.

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>