target/ppc: fix vextu[bhw][lr]x helpers

target/ppc: fix vextu[bhw][lr]x helpers

These helpers shouldn't depend on the host endianness, as they only use
shifts, ands, and int128_* methods.

Fixes: 60caf2216bf0 ("target-ppc: add vextu[bhw][lr]x instructions")
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
Message-Id: <20210826141446.2488609-3-matheus.ferst@eldorado.org.br>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>