build(changelog): add stm32mp13 and stm32mp15 scopes

The STM32MP1 series includes STM32MP13 and STM32MP15. As some features
may be dedicated to one SoC variant, add the 2 entries in the scopes
list.
While at it, correct the title for STM32MP1.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I521d0e1dfdda0638ab9970c93821cf08efbd183a
diff --git a/changelog.yaml b/changelog.yaml
index 1a11c9b..d07c4a0 100644
--- a/changelog.yaml
+++ b/changelog.yaml
@@ -485,12 +485,19 @@
           - plat/st
 
         subsections:
-          - title: ST32MP1
+          - title: STM32MP1
             scope: stm32mp1
 
             deprecated:
               - plat/st/stm32mp1
 
+            subsections:
+              - title: STM32MP13
+                scope: stm32mp13
+
+              - title: STM32MP15
+                scope: stm32mp15
+
       - title: Texas Instruments
         scope: ti