Upgrade AMD processor microcodes to mitigate the Spectre attack

Intel: https://tracker.debian.org/pkg/intel-microcode, https://bugs.debian.org/886367
- AMD: https://tracker.debian.org/pkg/amd64-microcode, https://bugs.debian.org/886382

Feature Branch: bugfix/15148-cpu-microcode-spectre

Related issues

Related to #14976 (closed)
Blocks #13245 (closed)
Blocks #15173 (closed)

Original created by @intrigeri on 15148 (Redmine)

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