Generate mod log names

[kasjer]

This adds "name:" to syscfg.logs nodes. This is optional log name.

With this change newt tool also generates file: \<bsp>-logcfg.c that contains function: const char *logcfg_log_module_name(uint8_t id)

that can be used to get module name for generated mod logs.

If name is not present like in this example:

syscfg.logs:
    BMA400_LOG:
        module: MYNEWT_VAL(BMA400_LOG_MODULE)
        level: MYNEWT_VAL(BMA400_LOG_LVL)

module name will be taken from BMA400_LOG by cutting off trailing _LOG to make it BMA400

[sjanc]

@m-gorecki please have a look