ext: hal: st: stm32cube: Add HAL for the STM32L1x series

This commit adds the STM32CUBE HAL for STM32L1x series MCUs.

Origin: ST Microelectronics
License: BSD-3-Clause
URL: http://www.st.com/en/embedded-software/stm32cubel1.html


Commit: 1.8.0
Purpose: HAL layer for STM32L1
Maintained-by: External

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>