xen/intr: remove xen_intr_alloc_and_bind_ipi() from !x86

[ehem_freebsd_m5p.com]

Summary

xen_intr_alloc_and_bind_ipi() is strictly used on x86, other
architectures do not need the function. The functionality is tied to
the core of the Xen interrupt handling and thus needs to remain in
sys/xen/xen_intr.c.

[ehem_freebsd_m5p.com]

Appears xen_intr_alloc_and_bind_ipi() was originally pulled to make getting things working easier. Appears it does in fact build on other architectures, but it isn't needed elsewhere. One can argue for or against pulling it on other architectures.

[ehem_freebsd_m5p.com]

Moving the declaration removal to D30605. Though this does really make D30605 and D29913 rather small. Used to be larger until the PVHv1 removal.

[ehem_freebsd_m5p.com]

Obsoleted by other work.