Improve Tegra detection.

[maleadt]

/etc/nv_tegra_release may not exist -- it didn't on specific Jetpack versions, and also doesn't on Nix -- so try some more things to detect Tegra.

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (275c9bc) 71.34% compared to head (6f65bba) 71.34%.

Files	Patch %	Lines
lib/cudadrv/version.jl	62.50%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2251      +/-   ##
==========================================
- Coverage   71.34%   71.34%   -0.01%     
==========================================
  Files         155      155              
  Lines       14851    14858       +7     
==========================================
+ Hits        10596    10600       +4     
- Misses       4255     4258       +3     

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