target/ppc: Implement vclzdm/vctzdm instructions

target/ppc: Implement vclzdm/vctzdm instructions

The signature of do_cntzdm is changed to allow reuse as GVecGen3i.fni8.
The method is also moved out of #ifdef TARGET_PPC64, as PowerISA doesn't
say vclzdm and vctzdm are 64-bit only.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Luis Pires <luis.pires@eldorado.org.br>
Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
Message-Id: <20211104123719.323713-3-matheus.ferst@eldorado.org.br>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>