Upgrade buildroot and kernel minor version

[afbjorklund]

http://lists.busybox.net/pipermail/buildroot/2020-October/294451.html

Our configuration still has a 4.19 kernel, rather than the default 5.4 kernel

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[afbjorklund]

Would be nice to get #9394 in before this one, to restore the kernel config along with bumping the minor version

I used the same kernel version as buildroot did (for 4.19), but I'm not sure how much it matters (150 vs 152 etc).

[afbjorklund]

Did some basic smoke testing locally, seemed OK

🐳 Preparing Kubernetes v1.19.2 on Docker 19.03.13 ..

🎁 Preparing Kubernetes v1.19.2 on CRI-O 1.18.3 ...

Linux minikube 4.19.150 #1 SMP Thu Oct 22 21:56:19 CEST 2020 x86_64 GNU/Linux

[codecov-io]

Codecov Report

Merging #9523 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #9523   +/-   ##
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  Coverage   29.11%   29.11%           
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  Files         172      172           
  Lines       10461    10461           
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  Hits         3046     3046           
  Misses       6990     6990           
  Partials      425      425