KVM: arm64: Move SVE state mapping at HYP to finalize-time

We currently map the SVE state to HYP on detection of a PID change.
Although this matches what we do for FPSIMD, this is pretty pointless
for SVE, as the buffer is per-vcpu and has nothing to do with the
thread that is being run.

Move the mapping of the SVE state to finalize-time, which is where
we allocate the state memory, and thus the most logical place to
do this.

Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>