cs: implement GetFirmwareVersion command

libraries/libstratosphere/include/stratosphere/cs/cs_command_processor.hpp

@@ -25,6 +25,8 @@ namespace ams::cs {
     class CommandProcessor : public scs::CommandProcessor {
         public:
             virtual bool ProcessCommand(const CommandHeader &header, const u8 *body, s32 socket) override;
+        private:
+            static void SendFirmwareVersion(s32 socket, const CommandHeader &header);
     };
 
 }