drm/radeon: restore modeset late in GPU reset path

Modeset path seems to conflict sometimes with the memory management
leading to kernel deadlock. This move modesetting reset after GPU
acceleration reset.

Signed-off-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org