boards: arm: add initial support for NUCLEO-L152RE board

The board features a STM32L152RET6 MCU.

Tested samples:

    * hello_world
    * basic/blinky
    * basic/button
    * gui/lvgl + SHIELD=ssd1306_128x64
    * philosophers
    * sensor/hmc5883l
    * subsys/shell/shell_module + CONFIG_EEPROM_SHELL=y
    * synchronization

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>