KVM: arm64: gic-v5: Mandate architected PPI for PMU emulation on GICv5

KVM: arm64: gic-v5: Mandate architected PPI for PMU emulation on GICv5

Make it mandatory to use the architected PPI when running a GICv5
guest. Attempts to set anything other than the architected PPI (23)
are rejected.

Additionally, KVM_ARM_VCPU_PMU_V3_INIT is relaxed to no longer require
KVM_ARM_VCPU_PMU_V3_IRQ to be called for GICv5-based guests. In this
case, the architectued PPI is automatically used.

Documentation is bumped accordingly.

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/20260319154937.3619520-33-sascha.bischoff@arm.com
Signed-off-by: Marc Zyngier <maz@kernel.org>