iwlwifi: Add fw_name_pre_rf_next_step to support different rf steps

Integrated chip may have different HW and RF steps.
Currently, the driver supports only different HW steps.
Add logic to support different RF steps enables combining different
HW and RF steps.

Signed-off-by: Haim Dreyfuss <haim.dreyfuss@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>