Added
- Add `--vmm-type=ec2` to calculate SNP measurements according to the EC2 VMM, which is slightly different than the way QEMU measures the initial VM state (by [agraf](https://github.com/agraf)).
Modified
- Detect OVMF that doesn't support kernel hashes and exit with error.
- Exit with error if `--initrd`/`--append` are used without `--kernel`.