manifest: update mcuboot

MCUboot was synchronized up to upstream:
1270880d2f717f9019742f5c450441aaf0504164

- boot_serial: refactoring and optimalization (mainly afects
  progressive erase implementation)
- migrate includes to <zephyr/...>
- switched DFU detection GPIO-pin configuration to be done through DTS.
  That pin is assigned thanks to `mcuboot-button0` pin-alias.
- boot_serial: Fix echo command code no longer compiling
- Added MCUboot status callback support, see `CONFIG_MCUBOOT_ACTION_HOOKS`
  Kconfig option.
- reworked LED usage, prefer DTS mcuboot-led0 alias over bootloader-led0
  alias
- Added initial support for leverage RAM-LOAD mode with the zephyr-rtos
  port
- boot_serial: Upgrade from cddl-gen 0.1.0 to zcbor 0.4.0

- imgtool: Added support for providing the signature by 3rd party

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