drm/radeon: add GPU reset flags

The idea here is to move to a finer grained reset.
In some cases we may not need reset every block, and
in other cases we may not need to re-init the entire
asic.

Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>