dt-bindings: ata: Add 'ata-generic' binding

The 'ata-generic' binding has been around since 2008, but never
documented.

Cc: Alexander Shiyan <shc_work@mail.ru>
Acked-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Link: https://lore.kernel.org/r/20221011135849.2785834-1-robh@kernel.orgSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/ata/ata-generic.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/ata/ata-generic.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Generic Parallel ATA Controller
+
+maintainers:
+  - Linus Walleij <linus.walleij@linaro.org>
+
+description:
+  Generic Parallel ATA controllers supporting PIO modes only.
+
+properties:
+  compatible:
+    items:
+      - enum:
+          - arm,vexpress-cf
+          - fsl,mpc8349emitx-pata
+      - const: ata-generic
+
+  reg:
+    items:
+      - description: Command interface registers
+      - description: Control interface registers
+
+  reg-shift:
+    enum: [ 1, 2 ]
+
+  interrupts:
+    maxItems: 1
+
+  ata-generic,use16bit:
+    type: boolean
+    description: Use 16-bit accesses instead of 32-bit for data transfers
+
+  pio-mode:
+    description: Maximum ATA PIO transfer mode
+    $ref: /schemas/types.yaml#/definitions/uint32
+    maximum: 6
+    default: 0
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    compact-flash@1a000 {
+        compatible = "arm,vexpress-cf", "ata-generic";
+        reg = <0x1a000 0x100>,
+              <0x1a100 0xf00>;
+        reg-shift = <2>;
+    };
+...