target/ppc: Implement Vector Extract Mask

target/ppc: Implement Vector Extract Mask

Implement the following PowerISA v3.1 instructions:
vextractbm: Vector Extract Byte Mask
vextracthm: Vector Extract Halfword Mask
vextractwm: Vector Extract Word Mask
vextractdm: Vector Extract Doubleword Mask
vextractqm: Vector Extract Quadword Mask

Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20211203194229.746275-3-matheus.ferst@eldorado.org.br>
Signed-off-by: Cédric Le Goater <clg@kaod.org>