KVM: arm64: Allow ARM64_PTR_AUTH when ARM64_VHE=n

We currently prevent PtrAuth from even being built if KVM is selected,
but VHE isn't. It is a bit of a pointless restriction, since we also
check this at run time (rejecting the enabling of PtrAuth for the
vcpu if we're not running with VHE).

Just drop this apparently useless restriction.

Acked-by: Andrew Scull <ascull@google.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>