The log context in zephyr is per file or module.
To use zephyr logging api, LOG_MODULE_REGISTER is used
to register a log context, LOG_MODULE_DECLARE is used
to refer to the registered context.
For function in header file, LOG_MODULE_DECLARE should
be used within that function to avoid context collapse,
a condition one source file have multiple context
registered or declared.
Signed-off-by: Chao Song <chao.song@linux.intel.com>