esp32: Make default SDMMC slot configurable.

Resolves part of micropython#18984. On ESP32-P4, SDMMC slot 0
supports SDIO 3.0, and is liekly the default for
most boards. MICROPY_HW_SDMMC_DEFAULT_SLOT can be
set in mpconfigboard.h to change default slot.

Signed-off-by: Dryw Wade <dryw.wade@sparkfun.com>

Author: sfe-SparkFro

ports/esp32/machine_sdcard.c

@@ -214,7 +214,7 @@ static mp_obj_t machine_sdcard_make_new(const mp_obj_type_t *type, size_t n_args
         ARG_freq,
     };
     #if SOC_SDMMC_HOST_SUPPORTED
-    static const int DEFAULT_SLOT = 1;
+    static const int DEFAULT_SLOT = MICROPY_HW_SDMMC_DEFAULT_SLOT;
     #else
     static const int DEFAULT_SLOT = SD_SLOT_MAX;
     #endif

ports/esp32/mpconfigport.h

@@ -195,6 +195,13 @@
 #ifndef MICROPY_HW_ENABLE_SDCARD
 #define MICROPY_HW_ENABLE_SDCARD            (1)
 #endif
+#ifndef MICROPY_HW_SDMMC_DEFAULT_SLOT
+#if CONFIG_IDF_TARGET_ESP32P4
+#define MICROPY_HW_SDMMC_DEFAULT_SLOT       (0)
+#else
+#define MICROPY_HW_SDMMC_DEFAULT_SLOT       (1)
+#endif
+#endif
 #define MICROPY_HW_SOFTSPI_MIN_DELAY        (0)
 #define MICROPY_HW_SOFTSPI_MAX_BAUDRATE     (esp_rom_get_cpu_ticks_per_us() * 1000000 / 200) // roughly
 #ifndef MICROPY_HW_ESP_NEW_I2C_DRIVER