iwlwifi: bump FW API to 66 for AX devices

Start supporting API version 66 for AX devices.

Th iwlwifi FW API is frozen every 6 weeks, so we need to bump the
newest version number that the driver supports accordingly.  In this
specific case, support for new HW will only be possible with the new
FW version.  This change still keeps backwards compatibility with
older FW API versions for existing devices.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210901101412.300012-1-luca@coelho.fi