target/ppc: Implement cnttzdm

target/ppc: Implement cnttzdm

Implement the following PowerISA v3.1 instruction:
cnttzdm: Count Trailing Zeros Doubleword Under Bit Mask

Suggested-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: <20211029202424.175401-9-matheus.ferst@eldorado.org.br>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>