target/ppc: Optimize emulation of vclzd instruction

target/ppc: Optimize emulation of vclzd instruction

Optimize Altivec instruction vclzd (Vector Count Leading Zeros Doubleword).
This instruction counts the number of leading zeros of each doubleword element
in source register and places result in the appropriate doubleword element of
destination register.

Using tcg-s count leading zeros instruction two times(once for each
doubleword element of source register vB) and placing result in
appropriate doubleword element of destination register vD.

Signed-off-by: Stefan Brankovic <stefan.brankovic@rt-rk.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <1563200574-11098-6-git-send-email-stefan.brankovic@rt-rk.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>