KVM: arm64: Revamp vgic maintenance interrupt configuration

KVM: arm64: Revamp vgic maintenance interrupt configuration

We currently don't use the maintenance interrupt very much, apart
from EOI on level interrupts, and for LR underflow in limited cases.

However, as we are moving toward a setup where active interrupts
can live outside of the LRs, we need to use the MIs in a more
diverse set of cases.

Add a new helper that produces a digest of the ap_list, and use
that summary to set the various control bits as required.

This slightly changes the way v2 SGIs are handled, as they used to
count for more than one interrupt, but not anymore.

Tested-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Tested-by: Mark Brown <broonie@kernel.org>
Link: https://msgid.link/20251120172540.2267180-22-maz@kernel.org
Signed-off-by: Oliver Upton <oupton@kernel.org>