iwlwifi: mvm: read and parse SKU ID if available

In v5 of the ALIVE notification, we may receive the SKU ID of the
device in use.  Read and store it locally for future access.  This
will be needed to find the correct PNVM (platform NVM) to pass to the
firmware.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/iwlwifi.20201008180656.798744ad514e.Ibb0d88586a34acc904bf319974d791faafb7a905@changeid