wifi: iwlwifi: mvm: prepare the introduction of V9 of REDUCED_TX_POWER

wifi: iwlwifi: mvm: prepare the introduction of V9 of REDUCED_TX_POWER

* Rename iwl_dev_tx_power_cmd to iwl_dev_tx_power_cmd_v3_v8
* struct iwl_dev_tx_power_common needs to be packed. It was always the
  case, but now that its size is not a multiple of 4, it becomes
  meaningful.
* Move per_band data out of the common structure since it won't be
  present in the new versions of the command.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20240729201718.8da29a66984f.I922bdef4740d990f98cb452e858c4157bbc491c5@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>