dts: Move to 'zephyr,memory-attr'

Move to 'zephyr,memory-attr' and use the newly introduced helpers.

Signed-off-by: Carlo Caione <ccaione@baylibre.com>

dts/bindings/base/zephyr,memory-region.yaml

@@ -5,7 +5,7 @@ description: Compatible for devices resulting in linker memory regions
 
 compatible: "zephyr,memory-region"
 
-include: base.yaml
+include: [base.yaml, "zephyr,memory-attr.yaml"]
 
 properties:
   zephyr,memory-region:
@@ -16,17 +16,3 @@ properties:
       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.
-
-  zephyr,memory-region-mpu:
-    type: string
-    enum:
-      - "RAM"
-      - "RAM_NOCACHE"
-      - "FLASH"
-      - "PPB"
-      - "IO"
-      - "EXTMEM"
-    description: |
-      Signify that this node should result in a dedicated MPU region. The
-      region address and size are taken from the <reg> property, while the MPU
-      attribute is the value of this property.