flash: add function to release flash device

include/flash.h

@@ -18,6 +18,7 @@ struct flash_dev {
 };
 
 struct flash_dev *flash_probe(void);
+void flash_release(struct flash_dev *dev);
 int flash_read(struct flash_dev *dev, uint32_t addr, void *data, size_t len);
 int flash_write(struct flash_dev *dev, uint32_t addr, const void *data,
 	size_t len);

source/drivers/sandbox_flash.c

@@ -113,3 +113,18 @@ err_free_dev:
 	free(dev);
 	return NULL;
 }
+
+void flash_release(struct flash_dev *dev)
+{
+	struct stdio_flash_priv *priv;
+
+	if (!dev)
+		return;
+
+	priv = dev->priv;
+
+	munmap(priv->data, priv->size);
+	fclose(priv->fp);
+	free(dev->priv);
+	free(dev);
+}