[question] extract the feature bits width to 4

[gengdongjiu]

> 
> Well, if the feature is not going to be upstream, the change may not be accepted.
> You could always add your custom code for "matching" the capability, like for e.g,
> ARM64_HAS_VIRT_HOST_EXTN.
Ok, Suzuki, thanks for your suggestion and answer.

> 
> Cheers
> Suzuki
> 
> .
>