docs(maintainers): update ST platform ports title

STM32MP1 is no more the only product to be supported in TF-A with the
new STM32MP2. Change "STM32MP1 platform port" to "STMicroelectronics
platform ports" to better reflect this.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I30b1fd4310d38092e3e815cb635b474fc84bdc30
diff --git a/docs/about/maintainers.rst b/docs/about/maintainers.rst
index 1025af2..d6027dc 100644
--- a/docs/about/maintainers.rst
+++ b/docs/about/maintainers.rst
@@ -800,8 +800,8 @@
 :|G|: `jwerner-chromium`_
 :|F|: plat/rockchip/
 
-STM32MP1 platform port
-^^^^^^^^^^^^^^^^^^^^^^
+STMicroelectronics platform ports
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 :|M|: Yann Gautier <yann.gautier@st.com>
 :|G|: `Yann-lms`_
 :|F|: docs/plat/st/*