xen: move x86-specific xen_vector_callback_enabled to sys/x86

[ehem_freebsd_m5p.com]

Summary

This appears x86-only and so should not be in the common area.

Adapted-to-HEAD-by: Elliott Mitchell <[e-mail]>

[royger]

LGTM, we should make this a bool type also.

[royger]

Also, the 'Adapted-to-HEAD-by' tag is not really a standard tag, and doesn't mention the original author either. I would just add a line saying:

"Based on the original work done by ..."

[ehem_freebsd_m5p.com]

In D29040#650635, @royger wrote:

Also, the 'Adapted-to-HEAD-by' tag is not really a standard tag, and doesn't mention the original author either. I would just add a line saying:

"Based on the original work done by ..."

This is differing behavior between Phabricator and other source review tools (such as Gerrit). Tools which follow git more closely the "Author:" header is preserved, pointing at the original author and date; and the person doing the adapting gets their name out as "Committer" or an extra tag. I see strengths and weaknesses in both approaches, Phabricator supports more source control tools and thus cannot closely match a typical git workflow.

This will need adjustment for bunches of these patches. D29040-D29043 are Julien Grall commits. D28982 is purely my work which came up during the forward-port process.