manifest: mcuboot: synch up to 680ed07

* MCUboot was build only for frdm_k64f in zephyr CI.
Extended Zephyr-RTOS integration platform by nrf52840dk_nrf52840
and nrf52840dongle_nrf52840 which allow to build MCUBoot on
these platform in Zephyr-RTOS CI.

* Added AES256 support for image encryption
* zephyr: serial: Remove unnecessary call to irq_unlock
* boot_serial: Port encoding to use cddl-gen
* bootutil_public: Make boot_read_swap_state declaration public

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