KVM: Clarify capability requirements for KVM_ARM_VCPU_FINALIZE

Userspace is only supposed to use KVM_ARM_VCPU_FINALIZE when there
is some vcpu feature that can actually be finalized.

This means that documenting KVM_ARM_VCPU_FINALIZE as available or
not depending on the capabilities present is not helpful.

This patch amends the documentation to describe availability in
terms of which capability is required for each finalizable feature
instead.

In any case, userspace sees the same error (EINVAL) regardless of
whether the given feature is not present or KVM_ARM_VCPU_FINALIZE
is not implemented at all.

No functional change.

Suggested-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

Documentation/virtual/kvm/api.txt

@@ -3999,17 +3999,16 @@ userspace should not expect to get any particular value there.
 
 4.119 KVM_ARM_VCPU_FINALIZE
 
-Capability: KVM_CAP_ARM_SVE
 Architectures: arm, arm64
 Type: vcpu ioctl
 Parameters: int feature (in)
 Returns: 0 on success, -1 on error
 Errors:
   EPERM:     feature not enabled, needs configuration, or already finalized
-  EINVAL:    unknown feature
+  EINVAL:    feature unknown or not present
 
 Recognised values for feature:
-  arm64      KVM_ARM_VCPU_SVE
+  arm64      KVM_ARM_VCPU_SVE (requires KVM_CAP_ARM_SVE)
 
 Finalizes the configuration of the specified vcpu feature.