A number of ESP-IDF header files that are needed to compile RIOT include the header file `driver/gpio.h` only because of the definition of the type `gpio_num_t`. However, this header file contains the entire GPIO API definition of the ESP-IDF, which conflicts with that of RIOT.
The solution was to use a wrapper library that does not need to include the `driver/gpio.h` file of the ESP-IDF during compilation of RIOT code.
This commit provides another approach which does not require such a wrapper library. It just provides its own `driver/gpio.h` in RIOT that is included by ESP-IDF header files instead of the original `driver/gpio.h` in ESP-IDF. It defines only the required `gpio_num_t` if RIOT code is compiled but includes the original `driver/gpio.h` of ESP-IDF if ESP-IDF code is compiled. This avoids to create a wrapper library for each module.
