logging: Add log initialization to system startup

Log API can be used before user can explicitly initialize the logger.
In order to ensure that logger core is ready to buffer log messages
it must be initialize as early as possible. Initialization does not
include initialization of default backend since driver may not be
ready and backend is needed only when log messages are processed.

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>
7 files changed