Set virtual grain on FreeBSD EC2 instances

[amendlik]

What does this PR do?

Set the virtual grain on FreeBSD EC2 instances running on AWS Nitro hypervisor.

What issues does this PR fix or reference?

Fixes: 61094

Previous Behavior

salt-call grains.get virtual
local:
    physical

New Behavior

salt-call grains.get virtual
local:
    Nitro

Merge requirements satisfied?

[NOTICE] Bug fixes or features added to Salt require tests.

• Docs
• Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• Tests written/updated

Commits signed with GPG?

Yes

Please review Salt's Contributing Guide for best practices.

See GitHub's page on GPG signing for more information about signing commits with GPG.

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Detected Issues (click me)

[INFO] Initializing environment for https://github.com/saltstack/pip-tools-compile-impersonate.
[INFO] Initializing environment for https://github.com/asottile/pyupgrade.
[INFO] Initializing environment for https://github.com/saltstack/pre-commit-remove-import-headers.
[INFO] Initializing environment for https://github.com/s0undt3ch/salt-rewrite.
[INFO] Initializing environment for https://github.com/timothycrosley/isort.
[INFO] Initializing environment for https://github.com/timothycrosley/isort:toml.
[INFO] Initializing environment for https://github.com/psf/black.
[INFO] Initializing environment for https://github.com/asottile/blacken-docs.
[INFO] Initializing environment for https://github.com/asottile/blacken-docs:black==21.7b0.
[INFO] Initializing environment for https://github.com/PyCQA/bandit.
[INFO] Initializing environment for https://github.com/saltstack/invoke-pre-commit.
[INFO] Initializing environment for https://github.com/saltstack/invoke-pre-commit:blessings,distro,jinja2,msgpack,pyyaml.
[INFO] Initializing environment for https://github.com/saltstack/mirrors-nox.
[INFO] Initializing environment for https://github.com/saltstack/mirrors-nox:pip>=20.2.4,<21.2,setuptools<58.0.
[INFO] Installing environment for https://github.com/saltstack/invoke-pre-commit.
[INFO] Once installed this environment will be reused.
[INFO] This may take a few minutes...
Check Known Missing Docstrings...........................................Passed
- hook id: invoke
- duration: 1.12s

---

Thanks again!

[Ch3LL]

this will require a changelog