drm/amdgpu: always force full reset for SOC21

There are cases where soft reset seems to succeed, but
does not, so always use mode1/2 for now.

Reviewed-by: Harish Kasiviswanathan <Harish.Kasiviswanathan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org