Change gpu Capability type to string

[crosbymichael]

This helps with mappings so that we are not translating multiple times
from caller to hook.

Signed-off-by: Michael Crosby crosbymichael@gmail.com

[codecov-io]

Codecov Report

Merging #2510 into master will decrease coverage by 4.03%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #2510      +/-   ##
=========================================
- Coverage   49.04%     45%   -4.04%     
=========================================
  Files          85      93       +8     
  Lines        7616    9583    +1967     
=========================================
+ Hits         3735    4313     +578     
- Misses       3189    4575    +1386     
- Partials      692     695       +3

Flag	Coverage Δ
#linux	49.04% <ø> (ø)	⬆️
#windows	41.41% <ø> (?)

Impacted Files	Coverage Δ
snapshots/native/native.go	43.3% <0%> (-10%)	⬇️
oci/spec.go	60% <0%> (-9.24%)	⬇️
metadata/snapshot.go	45.8% <0%> (-8.96%)	⬇️
archive/compression/compression.go	43.93% <0%> (-8.9%)	⬇️
content/local/writer.go	52.63% <0%> (-7.37%)	⬇️
archive/tar.go	43.11% <0%> (-7.04%)	⬇️
metadata/containers.go	47.97% <0%> (-6.62%)	⬇️
metadata/images.go	58.46% <0%> (-4.7%)	⬇️
metadata/buckets.go	56.33% <0%> (-4.6%)	⬇️
metadata/adaptors.go	41.46% <0%> (-4.49%)	⬇️
... and 53 more

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[stevvooe]

LGTM

[dmcgowan]

LGTM