KVM: arm64: Unmap vLPIs affected by changes to GSI routing information

KVM: arm64: Unmap vLPIs affected by changes to GSI routing information

KVM's interrupt infrastructure is dodgy at best, allowing for some ugly
'off label' usage of the various UAPIs. In one example, userspace can
change the routing entry of a particular "GSI" after configuring
irqbypass with KVM_IRQFD. KVM/arm64 is oblivious to this, and winds up
preserving the stale translation in cases where vLPIs are configured.

Honor userspace's intentions and tear down the vLPI mapping if affected
by a "GSI" routing change. Make no attempt to reconstruct vLPIs if the
new target is an MSI and just fall back to software injection.

Tested-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20250523194722.4066715-5-oliver.upton@linux.dev
Signed-off-by: Marc Zyngier <maz@kernel.org>