Updates for 2.2.0-rc1 release

[travis]: https://travis-ci.org/mcu-tools/mcuboot

[license]: https://github.com/mcu-tools/mcuboot/blob/main/LICENSE

This is MCUboot version 2.1.0

This is MCUboot version 2.2.0-rc1

MCUboot is a secure bootloader for 32-bits microcontrollers. It defines a

common infrastructure for the bootloader and the system flash layout on

- Added support for retrieving hw embed private keys for image encryption

  (The private key can be retrieved from trusted sources like OTP, TPM.).

- Changed bootutil's order of events to verify the image header

  before checking the image.

- Added the bootloader state object to the bootutil

  boot_is_header_valid() function

- Added optional write block size checking to ensure expected

  sizes match what is available on the hardware.

- Added optional erase size checking to ensure expected sizes

  match what is available on the hardware.

- Added debug logs for zephyr to output discrepencies in erase

  and write block sizes in dts vs actual hardware configuration

  at run-time.

- When using swap with scratch, the image is now decrypted when copying from

  the scratch partition to the primary slot. Therefore, the sratch partition

  doesn't contain plaintext firmware data anymore.