wifi: rtl8xxxu: Add LED control code for RTL8723AU

By default the LED will blink when there is some activity.

This is only compile tested.

Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/73323811-aa58-a1be-7867-a5d45b7ae3d6@gmail.com