accel/habanalabs: save class in hdev

It is more concise than to pass it to device init. Once we will add the
accel class, then we won't need to change the function signatures.

Signed-off-by: Oded Gabbay <ogabbay@kernel.org>
Reviewed-by: Tomer Tayar <ttayar@habana.ai>
Reviewed-by: Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>