fix: Pi 400 Bluetooth - hold RTS deasserted across BT_ON power-on, require Read Local Version to sync, mini UART no flow control first

kernel/src/Drivers/Bluetooth/Hci.hpp

@@ -199,6 +199,11 @@ namespace Drivers::Bluetooth::Hci {
     void InitializeUart();
 
     Transport GetTransport();
+
+    // Bytes per second the host-to-controller link can carry: the UART's
+    // line rate (8N1), or 0 when the transport is not the bottleneck (USB).
+    uint32_t TransportBytesPerSecond();
+
     void SetVendor(Vendor vendor);
     Vendor GetVendor();