Added support for the stm32l0discovery board, with cortex-m0+

    * config/arm/boards/stm32l0discovery/board.cfg: Board config for
        stm32l0discovery
    * config/arm/boards/stm32l0discovery/boardsupport.c: Board support
        for stm32l0disc overy
    * config/arm/boards/stm32l0discovery/calibration: Calibration for
        stm32l0discovery
    * config/arm/chips/stm32l053/chip.cfg: Chip configuration for
        stm32l053
    * config/arm/chips/stm32l053/chip.ld: Linker script for stm32l053
    * config/arm/chips/stm32l053/chipsupport.c: Chip support for
        stm32l053
    * config/arm/chips/stm32l053/chipsupport.h: Chip support for
        stm32l053