wifi: iwlwifi: Separate reading and parsing of reduce power table

It enables to better handle error cases. Also save the image till the
end of the loading and only then free it.

Signed-off-by: Alon Giladi <alon.giladi@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230606103519.71e3b3e0e794.Ifbe69ad99a7e805eb70e09280365821eb146b1c9@changeid


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