samples: mcuboot_config: introduce MCUBOOT_LOG_MODULE macros

Introduce MCUBOOT_LOG_MODULE_REGISTER and MCUBOOT_LOG_MODULE_DECLARE.

- MCUBOOT_LOG_MODULE_REGISTER
    Register a new log module and add the current C file to it.

- MCUBOOT_LOG_MODULE_DECLARE
    Add the current C file to an existing log module.

Signed-off-by: Emanuele Di Santo <emdi@nordicsemi.no>

samples/mcuboot_config/mcuboot_config.template.h

@@ -90,6 +90,12 @@
  * If logging is enabled the following functions must be defined by the
  * platform:
  *
+ *    MCUBOOT_LOG_MODULE_REGISTER(domain)
+ *      Register a new log module and add the current C file to it.
+ *
+ *    MCUBOOT_LOG_MODULE_DECLARE(domain)
+ *      Add the current C file to an existing log module.
+ *
  *    MCUBOOT_LOG_ERR(...)
  *    MCUBOOT_LOG_WRN(...)
  *    MCUBOOT_LOG_INF(...)