dt-bindings: mtd: refactor NAND bindings and add nand-controller-legacy.yaml

The modern NAND controller binding requires NAND chips to be described as
child nodes of the controller, for example:

  nand-controller {
          ...
          nand@0 {
                  /* raw NAND chip properties */
          };
  };

However, many existing device trees place NAND chip properties directly
within the controller node because those controllers support only a single
chip. This layout is still widely used by older platforms and by other DT
consumers such as U-Boot. Migrating all existing users to the new layout
will take time.

Several kernel drivers, such as ams-delta.c, davinci_nand.c and
fsmc_nand.c, still expect the legacy layout where raw NAND properties are
defined in the controller node.

To support both layouts during the transition:

- Extract NAND chip-related properties into separate schemas
  (nand-property.yaml and raw-nand-property.yaml) from
  nand-chip.yaml and raw-nand-chip.yaml.
- Introduce nand-controller-legacy.yaml to allow both the
  legacy and modern layouts.
- Add a select condition in nand-controller.yaml to prevent
  node name pattern matching for fsl,* NAND controllers.

Keep compatibility with existing device trees while allowing gradual
migration to the modern binding structure.

Signed-off-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

Documentation/devicetree/bindings/mtd/nand-controller-legacy.yaml

@@ -0,0 +1,65 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mtd/nand-controller-legacy.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: NAND Controller Common Properties
+
+maintainers:
+  - Miquel Raynal <miquel.raynal@bootlin.com>
+  - Richard Weinberger <richard@nod.at>
+
+description: >
+  The NAND controller should be represented with its own DT node, and
+  all NAND chips attached to this controller should be defined as
+  children nodes of the NAND controller. This representation should be
+  enforced even for simple controllers supporting only one chip.
+
+  This is only for legacy nand controller, new controller should use
+  nand-controller.yaml
+
+properties:
+
+  "#address-cells":
+    const: 1
+
+  "#size-cells":
+    enum: [0, 1]
+
+  ranges: true
+
+  cs-gpios:
+    description:
+      Array of chip-select available to the controller. The first
+      entries are a 1:1 mapping of the available chip-select on the
+      NAND controller (even if they are not used). As many additional
+      chip-select as needed may follow and should be phandles of GPIO
+      lines. 'reg' entries of the NAND chip subnodes become indexes of
+      this array when this property is present.
+    minItems: 1
+    maxItems: 8
+
+  partitions:
+    type: object
+
+    required:
+      - compatible
+
+patternProperties:
+  "^nand@[a-f0-9]$":
+    type: object
+    $ref: raw-nand-chip.yaml#
+
+  "^partition@[0-9a-f]+$":
+    type: object
+    $ref: /schemas/mtd/partitions/partition.yaml#/$defs/partition-node
+    deprecated: true
+
+allOf:
+  - $ref: raw-nand-property.yaml#
+  - $ref: nand-property.yaml#
+
+# This is a generic file other binding inherit from and extend
+additionalProperties: true
+