wifi: iwlwifi: iwl-drv: refactor image loading a bit

Refactor some parts of the image loading to be able to
extend the code for external FSEQ image loading more
easily.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20241228223206.224ac6599bbe.Iadc1974d633eec09797522f7d3fa543ea18bd7f6@changeid


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