iwlwifi: update nmi register

In the 8000 HW family the register for forcing an NMI has
changed, so this allows to still be able to force an NMI
while taking into account the HW in order to write to the
correct register.

Signed-off-by: Liad Kaufman <liad.kaufman@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>