synch with upstream 5b7ed6a8

Synchronized up to:
https://github.com/mcu-tools/mcuboot/commit/5b7ed6a831b4156f43a24a6db0fbb15238182ac4


- Added LED support for signaling enter to the serial recovery mode
- Added boot delay/debonuce of serial detect pin.
- Fixed compilation warnings with ZEPHYR_LOG_MODE_MINIMAL
- Added optional check which prevents attempting to boot image that
has been build for different ROM address than a slot it currently
resides in. Check is enabled if image was signed with IMAGE_F_ROM_FIXED flag.

Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>