target/ppc: Implement Vector Expand Mask

target/ppc: Implement Vector Expand Mask

Implement the following PowerISA v3.1 instructions:
vexpandbm: Vector Expand Byte Mask
vexpandhm: Vector Expand Halfword Mask
vexpandwm: Vector Expand Word Mask
vexpanddm: Vector Expand Doubleword Mask
vexpandqm: Vector Expand Quadword Mask

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
Message-Id: <20211203194229.746275-2-matheus.ferst@eldorado.org.br>
Signed-off-by: Cédric Le Goater <clg@kaod.org>