KVM: arm64: vgic-v5: Hold config_lock while finalizing GICv5 PPIs

KVM: arm64: vgic-v5: Hold config_lock while finalizing GICv5 PPIs

Finalizing the PPI state is done without holding any lock, which
means that two vcpus can race against each other and have one zeroing
the state while another one is setting it, or even maybe using it.

Fixing this is done by:

- holding the config lock while performing the initialisation

- checking if SW_PPI has already been advertised, meaning that
  we have already completed the initialisation once

Reviewed-by: Sascha Bischoff <sascha.bischoff@arm.com>
Fixes: 8f1fbe2fd2792 ("KVM: arm64: gic-v5: Finalize GICv5 PPIs and generate mask")
Link: https://sashiko.dev/#/patchset/20260319154937.3619520-1-sascha.bischoff%40arm.com
Link: https://patch.msgid.link/20260401103611.357092-7-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>