[stm32] Add STM32CubeF4 libraries

Adds the latest verified compatible versions of STM32CubeF4's core
libraries.

stm32f4xx_hal_driver: v1.7.11
cmsis_device_f4: v2.6.6
cmsis_core: v5.4.0_cm4

Change-Id: Ie4a43f959dd7a6d69c640c25032dd3feae45a84c
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/39600
Commit-Queue: Varun Sharma <vars@google.com>
Reviewed-by: Yecheng Zhao <zyecheng@google.com>
diff --git a/.gitmodules b/.gitmodules
index 744de82..3028ac5 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -16,3 +16,12 @@
 	path = third_party/picotls/src
 	url = https://github.com/h2o/picotls.git
 	branch = master
+[submodule "third_party/stm32cubef4/cmsis_device_f4"]
+	path = third_party/stm32cubef4/cmsis_device_f4
+	url = https://github.com/STMicroelectronics/cmsis_device_f4.git
+[submodule "third_party/stm32cubef4/cmsis_core_cm4"]
+	path = third_party/stm32cubef4/cmsis_core_cm4
+	url = https://github.com/STMicroelectronics/cmsis_core.git
+[submodule "third_party/stm32cubef4/stm32f4xx_hal_driver"]
+	path = third_party/stm32cubef4/stm32f4xx_hal_driver
+	url = https://github.com/STMicroelectronics/stm32f4xx_hal_driver.git