arm64: gicv5: Add GICv5 virtual machine support

[sarah.walker2_arm.com]

Summary

Create virtual machine tables on device attachment. Add functions to create
and destroy VMs.

Sponsored by: Arm Ltd

[andrew]

sys/arm64/arm64/gicv5.c

433

This lock will be unneeded after moving the calling block

529

729–750

This should be before setting irs->irs_ready = true

781–796

We need to check if any of these are NULL as contigmalloc may return it even with M_WAITOK.

916

Do we need to hold the lock over the free calls? free(9) doesn't sleep, but it's best to not hold a mutex if we don't need to.

[sarah.walker2_arm.com]

Address review comments & rebase

[sarah.walker2_arm.com]

Fix VPET alignment

[sarah.walker2_arm.com]

Rebase