net/sfc: prepare to merge init logs with main log type

net/sfc: prepare to merge init logs with main log type

Conversion to dynamic logging done in the previous patches
makes it possible to simplify internal controls for init
logging. This patch allows to prepare for such a change.
It makes init-unrelated messages use NOTICE level so that
the following patch will be able to convert init logging
to use INFO level and remain silent by default.

Signed-off-by: Ivan Malov <ivan.malov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Andy Moreton <amoreton@solarflare.com>