mtd: nand: Introduce the ECC engine framework

Create a generic ECC engine framework. This is a base to instantiate ECC
engine objects.

If we really want to be generic, bindings must evolve, so here is the
new logic. The following three properties are mutually exclusive:
- The nand-no-ecc-engine boolean property is set and there is no
  ECC engine to retrieve.
- The nand-use-soft-ecc-engine boolean property is set and the core
  will force using the use of software correction.
- There is a nand-ecc-engine property pointing at a node which will
  act as ECC engine.

It the later case, the property may reference:
- The NAND chip node itself (for the on-die ECC case).
- The parent node if the NAND controller embeds an ECC engine.
- Any other node being an external ECC controller as well.

Signed-off-by: Miquel Raynal <[email protected]>
Link: https://lore.kernel.org/linux-mtd/[email protected]

drivers/mtd/nand/Kconfig

@@ -9,4 +9,12 @@ source "drivers/mtd/nand/onenand/Kconfig"
 source "drivers/mtd/nand/raw/Kconfig"
 source "drivers/mtd/nand/spi/Kconfig"
 
+menu "ECC engine support"
+
+config MTD_NAND_ECC
+       bool
+       depends on MTD_NAND_CORE
+
+endmenu
+
 endmenu

drivers/mtd/nand/Makefile

@@ -6,3 +6,5 @@ obj-$(CONFIG_MTD_NAND_CORE) += nandcore.o
 obj-y	+= onenand/
 obj-y	+= raw/
 obj-y	+= spi/
+
+nandcore-$(CONFIG_MTD_NAND_ECC) += ecc.o