spi: Extend the core to ease integration of SPI memory controllers

Some controllers are exposing high-level interfaces to access various
kind of SPI memories. Unfortunately they do not fit in the current
spi_controller model and usually have drivers placed in
drivers/mtd/spi-nor which are only supporting SPI NORs and not SPI
memories in general.

This is an attempt at defining a SPI memory interface which works for
all kinds of SPI memories (NORs, NANDs, SRAMs).

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Jagan Teki <jagan@openedev.com>
diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index dcd719f..9fbd267 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -18,6 +18,13 @@
 
 if DM_SPI
 
+config SPI_MEM
+	bool "SPI memory extension"
+	help
+	  Enable this option if you want to enable the SPI memory extension.
+	  This extension is meant to simplify interaction with SPI memories
+	  by providing an high-level interface to send memory-like commands.
+
 config ALTERA_SPI
 	bool "Altera SPI driver"
 	help