build(changelog): add stm32mp13 and stm32mp15 fdts scopes

Some fdts changes in STM32MP1 family can be dedicated to one SoC,
STM32MP13 or STM32MP15. Add the dedicated scopes.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I2d64244054251c1f89dfe1ebbf6ce9dac21d47b6

changelog.yaml

@@ -1051,6 +1051,13 @@ subsections:
             deprecated:
               - fdts stm32mp1
 
+            subsections:
+              - title: STM32MP13
+                scope: stm32mp13-fdts
+
+              - title: STM32MP15
+                scope: stm32mp15-fdts
+
       - title: PIE
         scope: pie