add support for CPU microcode updates

[bcressey]

Issue number:
N/A

Description of changes:
Adds support for updating AMD and Intel CPU microcode, using the Linux kernel's early loading feature.

Testing done:
Verified that microcode is loaded early on an x86_64 variant.

# dmesg|head -n1
[    0.000000] microcode: microcode updated early to revision 0x5003102, date = 2021-03-08

Verified that the expected license files are included on an x86_64 variant.

# ls -l /usr/share/licenses/microcode/
-rw-r--r--. 1 root root 3758 Nov 16 02:02 LICENSE.amd-ucode
-rw-r--r--. 1 root root 1677 Nov 16 02:02 LICENSE.intel-ucode
lrwxrwxrwx. 1 root root   17 Nov 16 02:02 LicenseRef-scancode-amd-linux-firmware-export -> LICENSE.amd-ucode
lrwxrwxrwx. 1 root root   19 Nov 16 02:02 LicenseRef-scancode-intel-mcu-2018 -> LICENSE.intel-ucode
-rw-r--r--. 1 root root  222 Nov 16 02:02 attribution.txt

Verified that the attribution file looks reasonable.

# cat /usr/share/licenses/microcode/attribution.txt
bottlerocket-x86_64-microcode - https://github.com/bottlerocket-os/bottlerocket/tree/develop/packages/microcode
SPDX-License-Identifier: LicenseRef-scancode-amd-linux-firmware-export AND LicenseRef-scancode-intel-mcu-2018

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.

[zmrow]

🐻

[cbgbt]

Nice! ⛵