wcn36xx: Add accessor macro HW_VALUE_PHY for PHY settings

Adds HW_VALUE_PHY(hw_value) an access macro that will be used to
extract a hardware specific PHY setting for a given channel.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200910150708.2179043-4-bryan.odonoghue@linaro.org