wcn36xx: Hook and identify RF_IRIS_WCN3680

If DT indicates we are dealing with a WCN3680 mark the rf_id field as
RF_IRIS_WCN3680 allowing for further chip-specific logic.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200829033846.2167619-3-bryan.odonoghue@linaro.org