Boot: Make MCUBoot logging optional

Add new MCUBOOT_LOG_LEVEL CMake variable to the MCUBoot configuration.
In a debug build the MCUBoot logging can be set to several levels.
The logging can also be entirely disabled and thus the code size can be
reduced. In case of a release build the value of MCUBOOT_LOG_LEVEL is
overridden and the logging is disabled in MCUBoot.

Change-Id: I55ad8f85fdd0921f07a9c156858fadecf81a7449
Signed-off-by: David Vincze <david.vincze@arm.com>
6 files changed