[ST] Feature add ot-stm32 submodule (#32888)

* create openthread submodule

* move ot-stm32 to the right ot commit and use ot-stm32 in gn

* move to the right ot sha1

* bump ot-stm32 to the right version

* add back last line in .gitmodules

Author: STYoannZamaron

.gitmodules

@@ -73,6 +73,11 @@
 	url = https://github.com/SiliconLabs/ot-efr32.git
 	branch  = matter_sve
 	platforms = silabs,silabs_docker
+[submodule "ot-stm32"]
+	path = third_party/openthread/ot-stm32
+	url = https://github.com/openthread/openthread
+        branch = eb6377f
+        platforms = stm32
 [submodule "third_party/openthread/ot-ifx"]
 	path = third_party/openthread/ot-ifx
 	url = https://github.com/Infineon/ot-ifx-release.git

src/platform/stm32/args.gni

@@ -25,6 +25,7 @@ chip_device_platform = "stm32"
 chip_with_lwip = false
 mbedtls_target = "${stm32_sdk_build_root}:mbedtls"
 openthread_external_mbedtls = mbedtls_target
+openthread_root = "${chip_root}/third_party/openthread/ot-stm32"
 
 # GLOBAL CONFIG
 chip_monolithic_tests = false