target/ppc: Optimize emulation of vclzw instruction

target/ppc: Optimize emulation of vclzw instruction

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

Counting is to be performed in four iterations of for loop(one for each
word elemnt of source register vB). Every iteration consists of loading
appropriate word element from source register, counting leading zeros
with tcg_gen_clzi_i32, and saving the result in appropriate word element
of destination register.

Signed-off-by: Stefan Brankovic <stefan.brankovic@rt-rk.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <1563200574-11098-7-git-send-email-stefan.brankovic@rt-rk.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>