stm32cube: Update build system to support stm32l0xx

Get stm32l0xx support ready in build system.
Provide minimal file inclusion to support stm32l0 based board
port.

Change-Id: Ieb572389955e9e79a6100a6b1df35d9d08322789
Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>
2 files changed