dt-bindings: memory: introduce DDR4

Introduce JEDEC compliant DDR bindings, that use new memory-props binding.

The DDR4 compatible can be made of explicit vendor names and part
numbers or be of the form "ddrX-YYYY,AAAA...-ZZ" when associated with an
SPD, where (according to JEDEC SPD4.1.2.L-6):
- YYYY is the manufacturer ID
- AAAA... is the part number
- ZZ is the revision ID

The former form is useful when the SDRAM vendor and part number are
known, for example, when memory is soldered on the board.
The latter form is useful when SDRAM nodes are created at runtime by
boot firmware that doesn't have access to static part number information.

Signed-off-by: Clément Le Goffic <clement.legoffic@foss.st.com>
Signed-off-by: Clément Le Goffic <legoffic.clement@gmail.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20251118-b4-ddr-bindings-v9-2-a033ac5144da@gmail.com
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>

Author: clegoffic

Documentation/devicetree/bindings/memory-controllers/ddr/jedec,ddr4.yaml

@@ -0,0 +1,34 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/memory-controllers/ddr/jedec,ddr4.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: DDR4 SDRAM compliant to JEDEC JESD79-4D
+
+maintainers:
+  - Krzysztof Kozlowski <krzk@kernel.org>
+
+allOf:
+  - $ref: jedec,sdram-props.yaml#
+
+properties:
+  compatible:
+    items:
+      - pattern: "^ddr4-[0-9a-f]{4},[a-z]{1,20}-[0-9a-f]{2}$"
+      - const: jedec,ddr4
+
+required:
+  - compatible
+  - density
+  - io-width
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    ddr {
+        compatible = "ddr4-00ff,azaz-ff", "jedec,ddr4";
+        density = <8192>;
+        io-width = <8>;
+    };