drm/radeon: do not hard reset GPU while freezing on r600/r700 family

Seems r600/r700 does not like hard reset while freezing for hibernation
(regression due to 274ad65c which itself
is a fix for hibernation on some GPU families). Until i can debug further
issue with r600, let just disable this for r600/r700 as they are very
similar family and bug affecting one likely affect the other.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>