iwlwifi: introduce Image Loader (IML) - new firmware image

In future devices a new image will be introduced - IML. The IML, image
loader, is loaded by the ROM, and as part of the new self-init flow,
loads the rest of the firmware images to the device.

Store the image, so the ROM can load it to the device.

Signed-off-by: Golan Ben Ami <golan.ben.ami@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>