Merge branch 'feature/esptool_flash_encryption' into 'master'

Merge branch 'feature/esptool_flash_encryption' into 'master'

Flash encryption support

Flash encryption support in build system, tooling

To come in future MR:
* On-device key generation on first boot (for production devices), need to finalise testing of bootloader entropy seeding.
* spi_flash_encrypted_write to support non-32-byte block writes (at least optionally.)
* I think a lot of the bootloader_support component can possibly be rolled into "spiflash" and other components, to use a common API.

See merge request !240