amdgpu: don't ask about CHASH just default it for now.

If we bump this up a level, we can ask about it, for now,
just default to what amdgpu does.

Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>