dt-bindings: Add Arm SMMUv3 PMCG binding

Add binding for the Arm SMMUv3 PMU. Each node represents a PMCG, and is
placed as a sibling node of the SMMU. Although the PMCGs registers may
be within the SMMU MMIO region, they are separate devices, and there can
be multiple PMCG devices for each SMMU (for example one for the TCU and
one for each TBU).
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/20211117144844.241072-2-jean-philippe@linaro.orgSigned-off-by: Will Deacon <will@kernel.org>

Documentation/devicetree/bindings/perf/arm,smmu-v3-pmcg.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/perf/arm,smmu-v3-pmcg.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Arm SMMUv3 Performance Monitor Counter Group
+
+maintainers:
+  - Will Deacon <will@kernel.org>
+  - Robin Murphy <robin.murphy@arm.com>
+
+description: |
+  An SMMUv3 may have several Performance Monitor Counter Group (PMCG).
+  They are standalone performance monitoring units that support both
+  architected and IMPLEMENTATION DEFINED event counters.
+
+properties:
+  $nodename:
+    pattern: "^pmu@[0-9a-f]*"
+  compatible:
+    oneOf:
+      - items:
+          - const: arm,mmu-600-pmcg
+          - const: arm,smmu-v3-pmcg
+      - const: arm,smmu-v3-pmcg
+
+  reg:
+    items:
+      - description: Register page 0
+      - description: Register page 1, if SMMU_PMCG_CFGR.RELOC_CTRS = 1
+    minItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  msi-parent: true
+
+required:
+  - compatible
+  - reg
+
+anyOf:
+  - required:
+      - interrupts
+  - required:
+      - msi-parent
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+    #include <dt-bindings/interrupt-controller/irq.h>
+
+    pmu@2b420000 {
+            compatible = "arm,smmu-v3-pmcg";
+            reg = <0x2b420000 0x1000>,
+                  <0x2b430000 0x1000>;
+            interrupts = <GIC_SPI 80 IRQ_TYPE_EDGE_RISING>;
+            msi-parent = <&its 0xff0000>;
+    };
+
+    pmu@2b440000 {
+            compatible = "arm,smmu-v3-pmcg";
+            reg = <0x2b440000 0x1000>,
+                  <0x2b450000 0x1000>;
+            interrupts = <GIC_SPI 81 IRQ_TYPE_EDGE_RISING>;
+            msi-parent = <&its 0xff0000>;
+    };