sound: Add new sampling rates 12000Hz and 24000Hz

[epilys]

These values were just merged upstream in oasis, let's add them.

https://github.com/oasis-tcs/virtio-spec/commit/37c6a406678a5ee891fdf5671298cb4fcfa517f2

Requirements

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• [x] All commits in this PR have Signed-Off-By trailers (with git commit -s), and the commit message has max 60 characters for the summary and max 75 characters for each description line.
• [x] All added/changed functionality has a corresponding unit/integration test.
• [x] All added/changed public-facing functionality has entries in the "Upcoming Release" section of CHANGELOG.md (if no such section exists, please create one).
• [x] Any newly added unsafe code is properly documented.

[epilys]

We don't use these rates at our supported rates currently, so a new release can wait for the time being.