Fix broken IsVTXDisabled detection on AMD CPU

[afbjorklund]

VMX is in FeatureNames, but SVM is in ExtraFeatureNames
This meant that detection always failed for SVM (AMD)

Thanks to user @hilbertxia

Description

The new library approach to cpuid introduced in 5a8ce1a was broken on AMD CPU (SVM).
Unfortunately it also disabled all tests that were in the previous file-based version 850e264

Related issue(s)

Closes #4669

[GordonTheTurtle]

Please sign your commits following these rules:
https://github.com/moby/moby/blob/master/CONTRIBUTING.md#sign-your-work
The easiest way to do this is to amend the last commit:

$ git clone -b "svm" git@github.com:afbjorklund/machine.git somewhere
$ cd somewhere
$ git commit --amend -s --no-edit
$ git push -f

Amending updates the existing PR. You DO NOT need to open a new one.

[tstromberg]

Thanks for sending this PR in. I'm excited to see this new bug get fixed for our users.

[tstromberg]

Is there any additional work required before this PR gets merged?

[shivakumargn]

I noticed this on a AMD/windows laptop. The fix provided is only in linux/darwin files.
Fix seems to be incomplete.

[afbjorklund]

Did you actually look at the change ?
It is in the Intel file, not in Linux/Darwin

[shivakumargn]

Sorry my bad. I had looked at the links to original files (_linux.go & _darwin.go) referred to in the pull description.
Thanks for the fix.

[afbjorklund]

Thanks!

[atomi]

I believe this closes #4709 as well.