flashchips: Add Spansion 25FL256S......0

The Spansion 25SFL256S supports 4BA through an extended address register,
a 4BA mode set by bit 7 of that register, or native 4BA instructions.
Enable the former only for now.

Unfortunately the S25SF256S uses another instruction to write the exten-
ded address register. So we add an override for the instruction byte.

Change-Id: I0a95a81dfe86434f049215ebd8477392391b9efc
Signed-off-by: Nico Huber <nico.h@gmx.de>
Tested-by: Michael Fuckner <michael@fuckner.net>
Reviewed-on: https://review.coreboot.org/25132
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>
diff --git a/flash.h b/flash.h
index 01ff5cd..8eb8a7b 100644
--- a/flash.h
+++ b/flash.h
@@ -232,6 +232,9 @@
 		uint16_t max;
 	} voltage;
 	enum write_granularity gran;
+
+	/* SPI specific options (TODO: Make it a union in case other bustypes get specific options.) */
+	uint8_t wrea_override; /**< override opcode for write extended address register */
 };
 
 struct flashrom_flashctx {