iwlwifi: debug flow cleanup

Cleanup of the debug flow by moving several flows to separate
functions to increase readability.  Three functions were created:

1. iwl_fw_get_prph_len - returns the size needed for periphery dump.
2. iwl_fw_dump_mem for - executes the memory dumping flow.
3. iwl_trans_get_fw_monitor_len - returns the size needed for monitor dump.

Signed-off-by: Shahar S Matityahu <shahar.s.matityahu@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>