Revert "drm/radeon: always apply pci shutdown callbacks"

This seems to break reboot on some evergreen systems.

bugs:
https://bugs.freedesktop.org/show_bug.cgi?id=99524
https://bugzilla.kernel.org/show_bug.cgi?id=192271



This reverts commit a481daa8.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org