This moves quite a few of the x86-specific variables into a structure
separate from struct xenisrc, a first step in breaking them off.
Ideally these would never have left sys/x86/xen, but breaking them off at
the same time as moving the main portion of the file would have been
The original version of this commit moved xi_activehi and xi_edgetrigger
into xen_arch_isrc, but their usages disappeared with
ac3ede5371af34b0a89fa72b7a5bb706457b99ad. As a result purge them
Other architectures (ARM) assigns interrupt vectors via other means, thus
having the vector number in the general structure makes no sense.
This was inspired by the work of Julien Grall <email@example.com>,
2015-10-20 09:14:56, but now only preserves the "xen_arch_intr_t" and
the addition of arch-intr.h.