Revert "drm/amdgpu: disable gfxoff for navy_flounder"

This reverts commit 9c9b17a7.
Newly released sdma fw (51.52) provides a fix for the issue.

Signed-off-by: Jiansong Chen <Jiansong.Chen@amd.com>
Reviewed-by: Kenneth Feng <kenneth.feng@amd.com>
Reviewed-by: Tao Zhou <tao.zhou1@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>