dts: bindings: zephyr,linker-region property

Introduce optional `zephyr,linker-region` property which signifies that
the node should result in a linker memory region and what the name of
that region should be. Property added to compatibles likely to result
in a linker memory region; 'mmio-sram', 'arm,itcm`, `arm,dtcm`,
`nxp,imx-itcm`, `nxp,imx-dtcm` and `fixed-partitions`.

Signed-off-by: Jordan Yates <jordan.yates@data61.csiro.au>

dts/bindings/base/mem-region.yaml

@@ -0,0 +1,13 @@
+# Copyright (c) 2021, CSIRO
+# SPDX-License-Identifier: Apache-2.0
+# Common fields for devices resulting in linker memory regions
+
+properties:
+  zephyr,memory-region:
+    type: string
+    required: false
+    description: |
+      Signify that this node should result in a dedicated linker script
+      memory region in the final executable. The region address and size
+      is taken from the <reg> property, while the name is the value of
+      this property.