There's no firmware support for CSI on 43907.
You can refer to WL Tool for Embedded 802.11 Systems: CYW43xx Technical Information to obtain information about parameters like rssi.
Here's another thread Access to WiFi PHY layer information such as channel state information (CSI), etc. dealing with the same.
I got that there is no firmware support for CSI. What if I create a special firmware myself that does supply CSI and I want to use that firmware commercially, do I need a special license for this?
Please contact local sales for further clarity regarding this issue.