arm64/gicv3: Initialize all ITS collections at attach time

[scottph]

Summary

When device drivers attach, they configure interrupts. We want to
target all interrupts to the boot cpu early on, and then shuffle
them at a later point. However, we use domain proximity
information to limit which cpus an ITS will target. To handle the
case where the boot cpu isn't in the ITS's proximity doman, we
locate all redistributors and configure all ITS collections at
attach time, so that we're ready to configure any interrupts.

Sponsored by: Ampere Computing

[scottph]

Another approach could be to just all interrupts to target the boot cpu, maybe before ap startup and maybe apply proximity restrictions after ap startup?

[scottph]

D28340's approach of letting all CPUs get targeted by an ITS removes the need for changing this initialization.