wifi: iwlwifi: define API for external FSEQ images

The firmware will support external FSEQ images, define the
necessary API for that. We're not yet using/shipping such,
so don't add code to load them for now.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20250424153620.4f5acc3dff6c.Ic559d90376945c78495352a0d24b1d44ef887f2d@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>