drm/amdgpu/gfx8: fix driver reload with KIQ

Drop the deactivation in KIQ init and drop the KCQ disabling
via KIQ.  We disable the MEC shortly after anyway, so there is
no need to wait for all of this.  Doing so seems to leave the
MEC in a bad way.

Tested-by: Michel Dänzer <michel.daenzer@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>