iwlwifi: create opmode/device dependencies

The older devices (pre-7000/3000 series) all only work with the
DVM opmode due to firmware availability, while newer ones will
only work with the MVM opmode for the same reason.

When building a driver that only has one of MVM or DVM, there's
no reason to build the device support and have the PCIe IDs for
all devices since they can't be used anyway, so avoid that.

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