target/ppc: Introduce REQUIRE_VSX macro

target/ppc: Introduce REQUIRE_VSX macro

Introduce the macro to centralize checking if the VSX facility is
enabled and handle it correctly.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Bruno Larsen (billionai) <bruno.larsen@eldorado.org.br>
Signed-off-by: Luis Pires <luis.pires@eldorado.org.br>
Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
Message-Id: <20211104123719.323713-11-matheus.ferst@eldorado.org.br>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>