Add STM32L1xx platform

[yn386]

I tried to port micropython to NUCLEO-L152RE and it works. So I would like to add STM32L1 platform.

I got source https://github.com/STMicroelectronics/STM32CubeL1 using fetch_from_upstream.sh. Platform version is v1.10.3.

[dpgeorge]

Thanks for the contribution. The import of the L1 Cube HAL files was merged in 3adfa546cc0e9b649bb7339b1b8353185da680b4

The L1 HAL utils fix was merged on branch work-F0-1.9.0+F4-1.16.0+F7-1.7.0+G0-1.5.1+G4-1.3.0+H7-1.6.0+L0-1.11.2+L1-1.10.3+L4-1.17.0+WB-1.10.0+WL-1.1.0 in commit a9f8fee7bb0cb4ac1b4ff719b6b5b285f613f352