linux-imx

fpga: dfl: make init callback optional

This patch makes init callback of sub features optional. With
this change, people don't need to prepare any empty init callback.

Signed-off-by: Wu Hao <hao.wu@intel.com>
Acked-by: Moritz Fischer <mdf@kernel.org>
Signed-off-by: Moritz Fischer <mdf@kernel.org>