drm/radeon: disable hard reset in hibernate for APUs

Fixes a hibernation regression on APUs.

Bug: https://bugzilla.kernel.org/show_bug.cgi?id=191571
Fixes: 274ad65c

 (drm/radeon: hard reset r600 and newer GPU when hibernating.)
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org