[cxx]: simple spi master class

* spi cxx unit test (CATCH-based, on host)
* added portmacro.h to driver mocking
* added simple testing app to write/read SPI,
  using an MPU9250

examples/cxx/experimental/experimental_cpp_component/host_test/gpio/main/gpio_cxx_test.cpp

@@ -10,6 +10,7 @@
 
 #include <stdio.h>
 #include "esp_err.h"
+#include "unity.h"
 #include "freertos/portmacro.h"
 #include "gpio_cxx.hpp"
 #include "test_fixtures.hpp"