manifest: MCUboot upgrade

MCUboot was synchronized to
https://github.com/mcu-tools/mcuboot/commit/ad1fb3dde2



doc: actualize zephyr-rtos port README
Kconfig: prefer swap move if scratch_partition not enabled
Kconfig: Explicitly select CONFIG_CRC for CONFIG_MCUBOOT_SERIAL

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