boards/xtensa/esp32: Enable SPI Flash's MTD block

This commit enables the SPI Flash's MTD block driver. This block
driver enables testing the SPI Flash device without any associated
filesystems.

Signed-off-by: Tiago Medicci Serrano <tiago.medicci@espressif.com>

boards/xtensa/esp32/common/src/esp32_board_spiflash.c

@@ -429,6 +429,13 @@ static int init_storage_partition(void)
       return ret;
     }
 
+  ret = ftl_initialize(0, mtd);
+  if (ret < 0)
+    {
+      syslog(LOG_ERR, "ERROR: Failed to initialize the FTL layer: %d\n",
+              ret);
+      return ret;
+    }
 #endif
 
   return ret;