docs: kvm: devices/arm-vgic-v3: enhance KVM_DEV_ARM_VGIC_CTRL_INIT doc

kvm_arch_vcpu_precreate() returns -EBUSY if the vgic is
already initialized. So let's document that KVM_DEV_ARM_VGIC_CTRL_INIT
must be called after all vcpu creations.
Signed-off-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210405163941.510258-6-eric.auger@redhat.com

Documentation/virt/kvm/devices/arm-vgic-v3.rst

@@ -228,7 +228,7 @@ Groups:
 
     KVM_DEV_ARM_VGIC_CTRL_INIT
       request the initialization of the VGIC, no additional parameter in
-      kvm_device_attr.addr.
+      kvm_device_attr.addr. Must be called after all VCPUs have been created.
     KVM_DEV_ARM_VGIC_SAVE_PENDING_TABLES
       save all LPI pending bits into guest RAM pending tables.