esp_vfs_fat_spiflash_format_rw_wl() function

- ESP_OK - ESP_ERR_NO_MEM: if memory can not be allocated - Other errors from esp_vfs_fat_spiflash_mount_rw_wl

This API can be called when the FAT is mounted / not mounted. If this API is called when the FAT isn't mounted (by calling esp_vfs_fat_spiflash_mount_rw_wl), this API will first mount the FAT then format it, then restore back to the original state.