habanalabs: Save context in a command buffer object

Future changes require using a context while handling a command buffer,
and thus need to save the context in the command buffer object.

Signed-off-by: Tomer Tayar <ttayar@habana.ai>
Reviewed-by: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>