target/ppc: Implement Vector Insert Word from GPR using Immediate insns

target/ppc: Implement Vector Insert Word from GPR using Immediate insns

Implements the following PowerISA v3.1 instructions:
vinsw: Vector Insert Word from GPR using immediate-specified index
vinsd: Vector Insert Doubleword from GPR using immediate-specified
       index

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
Message-Id: <20211104123719.323713-7-matheus.ferst@eldorado.org.br>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>