target/ppc: implement xscvqp[su]qz

target/ppc: implement xscvqp[su]qz

Implement the following PowerISA v3.1 instructions:
xscvqpsqz: VSX Scalar Convert with round to zero Quad-Precision to
           Signed Quadword
xscvqpuqz: VSX Scalar Convert with round to zero Quad-Precision to
           Unsigned Quadword

Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220330175932.6995-9-matheus.ferst@eldorado.org.br>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>