KVM: arm64: gic-v5: Probe for GICv5 device

KVM: arm64: gic-v5: Probe for GICv5 device

The basic GICv5 PPI support is now complete. Allow probing for a
native GICv5 rather than just the legacy support.

The implementation doesn't support protected VMs with GICv5 at this
time. Therefore, if KVM has protected mode enabled the native GICv5
init is skipped, but legacy VMs are allowed if the hardware supports
it.

At this stage the GICv5 KVM implementation only supports PPIs, and
doesn't interact with the host IRS at all. This means that there is no
need to check how many concurrent VMs or vCPUs per VM are supported by
the IRS - the PPI support only requires the CPUIF. The support is
artificially limited to VGIC_V5_MAX_CPUS, i.e. 512, vCPUs per VM.

With this change it becomes possible to run basic GICv5-based VMs,
provided that they only use PPIs.

Co-authored-by: Timothy Hayes <timothy.hayes@arm.com>
Signed-off-by: Timothy Hayes <timothy.hayes@arm.com>
Signed-off-by: Sascha Bischoff <sascha.bischoff@arm.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Link: https://patch.msgid.link/20260319154937.3619520-38-sascha.bischoff@arm.com
Signed-off-by: Marc Zyngier <maz@kernel.org>