docs: release-notes: Add additional fixes

  MCUboot is compiled without support for them

- Added support for devices that do not require erase prior to write operation.

- Add corrections to the max app size calculations.

- Fixed issue with swap using scratch mode that would cause the

  primary image to be corrupt and unbootable after an update if the

  device was rebooted whilst the scratch area was being erased.

- Fixed issue with serial recovery if canonical CBOR mode was

  enabled.

- Fixed issue with serial recovery set image state not checking

  primary slot images.

- Fixed issue with watchdog not being fed during flash erase

  operations, which could cause the watchdog to time out on long

  erase operations and prevent firmware updates from being possible.

## Version 2.1.0