dts: arm: add DTS binding for ARM MPU peripheral

Add DTS binding files for the ARM MPU, for both ARM
MPU architecture variants, ARMv7-M and ARMv8-M.

Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>

dts/bindings/mmu_mpu/arm,armv7m-mpu.yaml

@@ -0,0 +1,28 @@
+---
+title: ARMv7-M Memory Protection Unit
+version: 0.1
+
+description: >
+    This binding describes the ARMv7-M Memory Protection Unit (MPU).
+
+properties:
+    compatible:
+      category: required
+      type: string
+      description: compatible strings
+      constraint: "arm,armv7m-mpu"
+      generation: define
+
+    reg:
+      category: required
+      type: int
+      description: mmio register space
+      generation: define
+
+    arm,num-mpu-regions:
+      category: required
+      type: int
+      description: number of MPU regions supported by hardware
+      generation: define
+
+...

dts/bindings/mmu_mpu/arm,armv8m-mpu.yaml

@@ -0,0 +1,28 @@
+---
+title: ARMv8-M Memory Protection Unit
+version: 0.1
+
+description: >
+    This binding describes the ARMv8-M Memory Protection Unit (MPU).
+
+properties:
+    compatible:
+      category: required
+      type: string
+      description: compatible strings
+      constraint: "arm,armv8m-mpu"
+      generation: define
+
+    reg:
+      category: required
+      type: int
+      description: mmio register space
+      generation: define
+
+    arm,num-mpu-regions:
+      category: required
+      type: int
+      description: number of MPU regions supported by hardware
+      generation: define
+
+...