Added spi selecta, use to select chips

firmware/drivers/spi_selecta/spi_selecta.cpp

+#include <spi_selecta.hpp>
+
+std::vector<Ad7124_4*> Spi_selecta::devices;
+
+void Spi_selecta::register_device(Ad7124_4* dev){
+    if(devices.size() == 0){
+        //Maximum number of ADCs on the bus supported
+        devices.reserve(4);
+    }
+    devices.push_back(dev);
+    digitalWrite(dev->get_ncs_(), HIGH);
+    pinMode(dev->get_ncs_(), OUTPUT);
+    digitalWrite(dev->get_ncs_(), HIGH);
+    dev->deselect_();
+}
+
+void Spi_selecta::select_device(Ad7124_4* dev){
+    for(auto d: devices){
+        d->deselect_();
+    }
+    dev->select_();
+}
+
+void Spi_selecta::deselect_device(){
+    for(auto d: devices){
+        d->deselect_();
+    }
+}
\ No newline at end of file

firmware/drivers/spi_selecta/spi_selecta.hpp

+#ifndef SPI_SELECTA_INCLUDED
+#define SPI_SELECTA_INCLUDED
+
+#include <vector>
+#include <ad7124_4.hpp>
+
+struct Spi_selecta{
+    Spi_selecta();
+    ~Spi_selecta()=default;
+    Spi_selecta(const Spi_selecta&)=delete;
+
+    static std::vector<Ad7124_4*> devices;
+
+    static void register_device(Ad7124_4* dev);
+    static void select_device(Ad7124_4* dev);
+    static void deselect_device();
+};
+
+#endif
\ No newline at end of file