KVM: arm64: GICv2: Extract LR folding primitive

KVM: arm64: GICv2: Extract LR folding primitive

As we are going to need to handle deactivation for interrupts that
are not in the LRs, split vgic_v2_fold_lr_state() into a helper
that deals with a single interrupt, and the function that loops
over the used LRs.

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/20251120172540.2267180-18-maz@kernel.org
Signed-off-by: Oliver Upton <oupton@kernel.org>