synch with upstream c74c551e

Synchronized up to:
https://github.com/JuulLabs-OSS/mcuboot/commit/c74c551ed6fdd27935c9aaa307095869a44c8202



- corected bugfix #830 of upgrade issue in swap-move
- changed default for CONFIG_MCUBOOT_CLEANUP_ARM_CODE to n, added MPU register clean-up to this option
- bootutil: ecdsa: Fixed CC310 for nRF devices
- zephyr: made flash_area_erased_val() weak
- serial recovery: allow unaligned last image data chunk

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