mbed: Add enable MCUboot logging parameter and fix logging configuration

This commit add option for a user to enable MCUboot logging from project
configuration level.
Now, logging from MCUboot's sources will be printed in the same way as
mbed-os logs.
Co-created by @AGlass0fMilk - George Beckstein

Signed-off-by: Artur Tynecki <artur.tynecki@mobica.com>
Signed-off-by: George Beckstein <george.beckstein@gmail.com>