boards/esp32-ethernet-kit: add button definition

Conflicts with Ethernet phy clock input.

Tested with tests/saul:

Dev: BOOT	Type: SENSE_BTN
Data:	              0

Dev: BOOT	Type: SENSE_BTN
Data:	              1

and tests/buttons:

On-board button test

 -- Available buttons: 1

 -- Try pressing buttons to test.

[SUCCESS]
Pressed BTN0
Pressed BTN0
Pressed BTN0

boards/esp32-ethernet-kit-v1_0/include/board.h

@@ -33,6 +33,40 @@ static inline void board_init(void) {
     board_init_common();
 }
 
+#if !MODULE_ESP_ETH || DOXYGEN
+/**
+ * @name    Button pin definitions
+ * @{
+ */
+/**
+ * @brief   Default button GPIO pin definition
+ *
+ * The button is only available when Ethernet is not used, as is shares its pin
+ * with the Phy clock.
+ */
+#define BTN0_PIN        GPIO0
+
+/**
+ * @brief   Default button GPIO mode definition
+ *
+ * Since the GPIO of the button is pulled up with an external resistor, the
+ * mode for the GPIO pin has to be GPIO_IN.  */
+#define BTN0_MODE       GPIO_IN
+
+/**
+ * @brief   Default interrupt flank definition for the button GPIO
+ */
+#ifndef BTN0_INT_FLANK
+#define BTN0_INT_FLANK  GPIO_FALLING
+#endif
+
+/**
+ * @brief   Definition for compatibility with previous versions
+ */
+#define BUTTON0_PIN     BTN0_PIN
+/** @} */
+#endif /* !MODULE_ESP_ETH || DOXYGEN */
+
 /**
  * @name    ESP32 Ethernet (EMAC) configuration
  * @{

boards/esp32-ethernet-kit-v1_0/include/gpio_params.h

@@ -31,6 +31,14 @@ extern "C" {
  */
 static const  saul_gpio_params_t saul_gpio_params[] =
 {
+#ifndef MODULE_ESP_ETH
+    {
+        .name = "BOOT",
+        .pin = BTN0_PIN,
+        .mode = BTN0_MODE,
+        .flags = SAUL_GPIO_INVERTED
+    },
+#endif
 };
 
 #ifdef __cplusplus