Request: enable SNP_KERNEL_HASHES to include kernel/initrd in SEV-SNP launch measurement

## Summary

Enable `SNP_KERNEL_HASHES` in the OVMF build so that the kernel, initrd, and kernel command line are included in the AMD SEV-SNP launch measurement.

## Current behavior

The SNP `MEASUREMENT` on EC2 only covers the OVMF firmware. The kernel, initrd, and cmdline are not measured within the SEV-SNP boundary. Measuring the kernel requires NitroTPM, which lives outside the SEV-SNP trust boundary — there is no cryptographic link between the SNP attestation report and the NitroTPM quote, so a remote verifier cannot confirm the full boot chain using only AMD's root of trust.

The published OVMF in this repo is based on `edk2-stable202211`, which predates `SNP_KERNEL_HASHES` support in EDK2. Upstream EDK2 added this feature in later stable branches, allowing OVMF to include kernel, initrd, and cmdline hashes in the launch digest computed by the AMD PSP.

## What this would enable

With `SNP_KERNEL_HASHES` enabled, `sev-snp-measure` can compute the full launch measurement from (OVMF + kernel + initrd + cmdline), and a remote verifier can match it against the live attestation report. The entire boot chain becomes verifiable through the SNP report alone, without trusting any component outside the SEV-SNP boundary.

## Offer to contribute

We are happy to contribute patches, testing, or documentation to help make this happen. Is there a preferred way to collaborate on this?

Start by locating the OVMF build based on edk2-stable202211 and the point where SNP_KERNEL_HASHES can be configured. Review the later EDK2 stable-branch support and verify that the resulting SNP measurement includes the OVMF, kernel, initrd, and command line; done means the build works and sev-snp-measure matches the live attestation report.

Written by the indexing model from the issue text.