- Secure boot V2 verification failed when multiple keys are used to sign the bootloader
and the application is signed with a key other than the first key that is used to
sign the bootloader.
- The issue was introduced as a regression from the commit `ff16ce43`.
- Added a QEMU test for recreating the issue.
- Made SECURE_BOOT_FLASH_BOOTLOADER_DEFAULT independent of SECURE_BOOT_BUILD_SIGNED_BINARIES.