target/ppc: Implement Vector Insert from VSR using GPR index insns

target/ppc: Implement Vector Insert from VSR using GPR index insns

Implements the following PowerISA v3.1 instructions:
vinsbvlx: Vector Insert Byte from VSR using GPR-specified Left-Index
vinshvlx: Vector Insert Halfword from VSR using GPR-specified
          Left-Index
vinswvlx: Vector Insert Word from VSR using GPR-specified Left-Index
vinsbvrx: Vector Insert Byte from VSR using GPR-specified Right-Index
vinshvrx: Vector Insert Halfword from VSR using GPR-specified
          Right-Index
vinswvrx: Vector Insert Word from VSR using GPR-specified Right-Index

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
Message-Id: <20211104123719.323713-8-matheus.ferst@eldorado.org.br>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>