The default macros GPIO_PIN and GPIO_UNDEF do not have to be overridden. The GPIO_PIN macro definition was even wrong for 40 GPIOs without splitting into ports, even if that did not lead to erroneous behavior.
Although ESP32 has four SPI controllers, only two of them can be effectively used (HSP and VSPI). The third one (FSPI) is used for external memory such as flash and PSRAM and can not be used for peripherals. FSPI is therefore removed from the API. In addition, the SPI0_DEV and SPI1_DEV configuration parameters are renamed SPI0_CTRL and SPI1_CTRL to better describe what they define and to avoid confusion with SPI_DEV (0) and SPI_DEV (1).
cpu/esp32/include/periph_cpu.h overrides the default definition of adc_res_t from periph/adc with a definition which contains only four resolution, two new resolutions and two resolutions defined by the default definition of adc_res_t. This gives compilation errors if an application uses other resolutions. According to the documentation, adc_sample should return -1 if the resolution is not supported. All other CPUs override adc_res_t either to add new resolutions or to mark resolutions as unsupported. But they all allow to use them at the interface. Therefore, esp32 overrides now the definition of adc_res_t with all resolutions that are defined by the default definition of adc_res_t and new platform specific resolutions. It returns -1 if a resolution is used in adc_sample that is not supported.
