synch with upstream 296949ef

Synchronized up to:
https://github.com/JuulLabs-OSS/mcuboot/commit/@296949e



Improvements:
- hardening against hardware level fault injection and timing attacks
- Abstract crypto primitives to simplify porting.
- boot: Add ram-load upgrade mode
- renamed single-image mode to single-slot mode

- kconfig: provide logic for setting key file, simplify prj.conf

- imgtool: Print image digest during verify
- imgtool: Add possibility to set confirm flag for hex files as well
- imgtool: --confirm implies --pad

- Added single-slot Zephyr-RTOS test build

fixes:
- bootutil: fix boostrapping in swap-move
- bootutil: fix swap-move brick with padded image_0
- Disable HW stack protection (temporary hack)
- reset SPLIM registers before boot
- fixes build issue that occurs if CONF_FILE contains multiple file paths instead of single file path.
- imgtool: Fix 'custom_tlvs' argument handling
- Turn off cache for Cortex M7 before chain-loading.- hardening against hardware level fault injection and timing attacks

Conflicts:
- took upsteram boot/zephyr/sample.yaml

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