target/ppc: Replicate Double->Single-Precision result

target/ppc: Replicate Double->Single-Precision result

Power ISA v3.1 formalizes the previously undefined result in
words 1 and 3 to be a copy of the result in words 0 and 2.

This affects: xvcvsxdsp, xvcvuxdsp, xvcvdpsp.

And the previously undefined result in word 1 to be a copy of
the result in word 0.

This affects: xscvdpsp.

Signed-off-by: Lucas Coutinho <lucas.coutinho@eldorado.org.br>
Message-Id: <20220316200427.3410437-1-lucas.coutinho@eldorado.org.br>
Signed-off-by: Cédric Le Goater <clg@kaod.org>