add support for naming NAND banks

Requires users to name their nand banks, allowing them to be used
instead of bank numbers in script commands.

src/flash/nand.h

@@ -75,6 +75,7 @@ struct nand_ecclayout {
 
 struct nand_device
 {
+	char *name;
 	struct nand_flash_controller *controller;
 	void *controller_priv;
 	struct nand_manufacturer *manufacturer;