rpi: add support for pi 400 & pi 4B 8GB

[creativeprojects]

This PR adds support for the raspberry pi 400 board (tested on mine), and support for the 8GB RAM version of the pi 4B

Also:

• add unit tests for revision 1.2 of pi 4B boards (2 and 4GB)
• add unit tests for revision 1.4 of pi 4B boards (2, 4 and 8GB)
• add unit tests for pi 400 (revision 1.0)

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[codecov-commenter]

Codecov Report

Merging #11 (da7b9bb) into main (962178f) will increase coverage by 0.0%. The diff coverage is 100.0%.

@@          Coverage Diff          @@
##            main     #11   +/-   ##
=====================================
  Coverage   33.9%   33.9%           
=====================================
  Files         49      49           
  Lines       5376    5379    +3     
=====================================
+ Hits        1823    1826    +3     
  Misses      3427    3427           
  Partials     126     126           

Impacted Files	Coverage Δ
rpi/rpi.go	29.7% <100.0%> (+0.6%)	:arrow_up:

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[maruel]

You'll have to wait a bit for me to fix the CI.

[maruel]

Do you mind to git fetch, git rebase and git push -f again? The CI should be fixed now. Thanks!

[maruel]

Would you mind signing the CLA?

[creativeprojects]

@googlebot I signed it!

[googlebot]

CLAs look good, thanks!

ℹ️ Googlers: Go here for more info.

[maruel]

gohci

[maruel]

Oops ignore the failures, it's not your fault. Thanks!