add flash and PSRAM CS IO acquire function

components/esp32s2/include/esp32s2/spiram.h

@@ -78,6 +78,15 @@ size_t esp_spiram_get_size(void);
  */
 void esp_spiram_writeback_cache(void);
 
+/**
+ * @brief get psram CS IO
+ *
+ * This interface should be called after PSRAM is enabled, otherwise it will
+ * return an invalid value -1/0xff.
+ *
+ * @return psram CS IO or -1/0xff if psram not enabled
+ */
+uint8_t esp_spiram_get_cs_io(void);
 
 
 /**