dt-bindings: reserved-memory: Add support for DRAM MRQ GSCs

Add bindings for DRAM MRQ GSC support.
Co-developed-by: Stefan Kristiansson <stefank@nvidia.com>
Signed-off-by: Stefan Kristiansson <stefank@nvidia.com>
Signed-off-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

Documentation/devicetree/bindings/reserved-memory/nvidia,tegra264-bpmp-shmem.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/reserved-memory/nvidia,tegra264-bpmp-shmem.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Tegra CPU-NS - BPMP IPC reserved memory
+
+maintainers:
+  - Peter De Schrijver <pdeschrijver@nvidia.com>
+
+description: |
+  Define a memory region used for communication between CPU-NS and BPMP.
+  Typically this node is created by the bootloader as the physical address
+  has to be known to both CPU-NS and BPMP for correct IPC operation.
+  The memory region is defined using a child node under /reserved-memory.
+  The sub-node is named shmem@<address>.
+
+allOf:
+  - $ref: reserved-memory.yaml
+
+properties:
+  compatible:
+    const: nvidia,tegra264-bpmp-shmem
+
+  reg:
+    description: The physical address and size of the shared SDRAM region
+
+unevaluatedProperties: false
+
+required:
+  - compatible
+  - reg
+  - no-map
+
+examples:
+  - |
+    reserved-memory {
+       #address-cells = <2>;
+       #size-cells = <2>;
+       dram_cpu_bpmp_mail: shmem@f1be0000 {
+           compatible = "nvidia,tegra264-bpmp-shmem";
+           reg = <0x0 0xf1be0000 0x0 0x2000>;
+           no-map;
+       };
+    };
+...