iwlwifi: add HW step to new cfg device table

We need to use different firmware versions for different HW steps with
certain devices.  Prepare for this differentiation by adding HW step
to the new device table.

Change-Id: Ib1afb7b0c89e9dc2d26e6d32ea19e978c17ba1dd
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>