KVM: arm64: nv: Don't erroneously claim FEAT_DoubleLock for NV VMs

KVM: arm64: nv: Don't erroneously claim FEAT_DoubleLock for NV VMs

ID_AA64DFR0_EL1.DoubleLock is one of those annoying signed feature
fields where a non-negative value implies that a feature is implemented
and a negative value implies that it is not. While the intention of
masking this field was likely to hide the feature, KVM actually
advertises it, even on unsupporting hardware.

Remove FEAT_DoubleLock from the mask, making the NI value visible to the
VM. Take care to accept the old, incorrect values for this field as
we've lied to userspace.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>