dt-bindings: mtd: st,stm32: add MP25 support

Add a compatible string to support MP25 SoC.

FMC2 IP supports up to 4 chip select. On MP1 SoC, only 2 of them are
available when on MP25 SoC, the 4 chip select are available.

Signed-off-by: Christophe Kerello <[e-mail]>
Reviewed-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: Miquel Raynal <[e-mail]>
Link: https://lore.kernel.org/linux-mtd/[e-mail]

Documentation/devicetree/bindings/mtd/st,stm32-fmc2-nand.yaml

···
     enum:
       - st,stm32mp15-fmc2
       - st,stm32mp1-fmc2-nfc
+      - st,stm32mp25-fmc2-nfc
 
   reg:
     minItems: 6
-    maxItems: 7
+    maxItems: 12
 
   interrupts:
     maxItems: 1
···
             - description: Chip select 1 data
             - description: Chip select 1 command
             - description: Chip select 1 address space
+
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: st,stm32mp25-fmc2-nfc
+    then:
+      properties:
+        reg:
+          items:
+            - description: Chip select 0 data
+            - description: Chip select 0 command
+            - description: Chip select 0 address space
+            - description: Chip select 1 data
+            - description: Chip select 1 command
+            - description: Chip select 1 address space
+            - description: Chip select 2 data
+            - description: Chip select 2 command
+            - description: Chip select 2 address space
+            - description: Chip select 3 data
+            - description: Chip select 3 command
+            - description: Chip select 3 address space
 
 required:
   - compatible