Config: Add stm targets in single entry point

This patch allows to group all stm targets in single cmake entry point.
The stm TARGET_PLATFORM should prefix by "STM".
stm platforms supports CoreIPC, CoreIPCTfmLevel2 and RegressionIPCTfmLevel2
Build with GNUARM toolchain.

Change-Id: I6535420b2304c18f2ab260620c38fef632eb7488
Signed-off-by: Ludovic Barre <ludovic.barre@st.com>
Signed-off-by: Michel Jaouen <michel.jaouen@st.com>
diff --git a/docs/user_guides/tfm_integration_guide.rst b/docs/user_guides/tfm_integration_guide.rst
index 09e43a0..e4b56d1 100644
--- a/docs/user_guides/tfm_integration_guide.rst
+++ b/docs/user_guides/tfm_integration_guide.rst
@@ -28,6 +28,7 @@
 - Musca-S1 test chip board (Cortex-M33 SSE-200 subsystem)
 - CoreLink SSE-200 Subsystem for MPS3 (AN524)
 - DesignStart FPGA on Cloud: Cortex-M33 based platform (SSE-200_AWS)
+- STM32L5xx: Cortex-M33 based platform (STM32L562 and STM32L552 socs)
 
 The files related to the supported platforms are contained under the
 ``platform`` subfolder. The platform specific files are under
@@ -53,6 +54,9 @@
 More information about the SSE-200_AWS platform can be found in:
 `SSE-200_AWS product page <https://aws.amazon.com/marketplace/pp/ARM-DesignStart-FPGA-on-Cloud-Cortex-M33-based-pla/B082DMMTLW>`__
 
+More information about the STM32L5xx platform can be found in:
+`STM32L5 series product page <https://www.st.com/content/st_com/en/products/microcontrollers-microprocessors/stm32-32-bit-arm-cortex-mcus/stm32-ultra-low-power-mcus/stm32l5-series.html>`__
+
 Generic drivers and startup/scatter files
 =========================================
 The addition of a new platform means the creation of a new subfolder inside