sf: Enable FDT-based configuration and memory mapping

Enable device tree control of SPI flash, and use this to implement
memory-mapped SPI flash, which is supported on Intel chips.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/spi_flash.h b/include/spi_flash.h
index 030d49c..3b6a44e 100644
--- a/include/spi_flash.h
+++ b/include/spi_flash.h
@@ -39,6 +39,7 @@
 	/* Erase (sector) size */
 	u32		sector_size;
 
+	void *memory_map;	/* Address of read-only SPI flash access */
 	int		(*read)(struct spi_flash *flash, u32 offset,
 				size_t len, void *buf);
 	int		(*write)(struct spi_flash *flash, u32 offset,