dt-bindings: i3c: Add AST2600 i3c controller

Add a devicetree binding for the ast2600 i3c controller hardware. This
is heavily based on the designware i3c core, plus a reset facility
and two platform-specific properties:

 - sda-pullup-ohms: to specify the value of the configurable pullup
   resistors on the SDA line

 - aspeed,global-regs: to reference the (ast2600-specific) i3c global
   register block, and the device index to use within it.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> (on v1)
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20230331091501.3800299-3-jk@codeconstruct.com.auSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Documentation/devicetree/bindings/i3c/aspeed,ast2600-i3c.yaml

+# SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/i3c/aspeed,ast2600-i3c.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: ASPEED AST2600 i3c controller
+
+maintainers:
+  - Jeremy Kerr <jk@codeconstruct.com.au>
+
+allOf:
+  - $ref: i3c.yaml#
+
+properties:
+  compatible:
+    const: aspeed,ast2600-i3c
+
+  reg:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+  resets:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  sda-pullup-ohms:
+    enum: [545, 750, 2000]
+    default: 2000
+    description: |
+      Value to configure SDA pullup resistor, in Ohms.
+
+  aspeed,global-regs:
+    $ref: /schemas/types.yaml#/definitions/phandle-array
+    items:
+      - items:
+          - description: phandle to i3c global register syscon node
+          - description: index of this i3c controller in the global register set
+    description: |
+      A (phandle, controller index) reference to the i3c global register set
+      used for this device.
+
+required:
+  - compatible
+  - reg
+  - clocks
+  - interrupts
+  - aspeed,global-regs
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+
+    i3c-master@2000 {
+        compatible = "aspeed,ast2600-i3c";
+        reg = <0x2000 0x1000>;
+        #address-cells = <3>;
+        #size-cells = <0>;
+        clocks = <&syscon 0>;
+        resets = <&syscon 0>;
+        aspeed,global-regs = <&i3c_global 0>;
+        pinctrl-names = "default";
+        pinctrl-0 = <&pinctrl_i3c1_default>;
+        interrupts = <GIC_SPI 102 IRQ_TYPE_LEVEL_HIGH>;
+    };
+...