stm32cube: import stm32cube files for STM32L4xx

Import the STM32CUBE files that will be used for the support
of the STM32L4xx series.

The files were taken from stm32cube_fw_l4_v152.zip.

Origin: STM32CubeMX
URL: http://www.st.com/en/development-tools/stm32cubemx.html?icmp=stm32cubemx_pron_pr-stm32cubef2_apr2014&sc=stm32cube-pr2


Version: v152
Purpose: Introduction of STM32L4xx SoC definitions
Maintained-by: External

Change-Id: Ib33a86aa35168827ff2d47f0793554fe35945762
Signed-off-by: Fabien Parent <fparent@baylibre.com>