target/mips: Rename sa16 -> sa, bz_df -> bz -> bz_v

target/mips: Rename sa16 -> sa, bz_df -> bz -> bz_v

This 'shift amount' format is not always 16-bit, so name it
generically as 'sa'. This will help to unify the various
arg_msa decodetree generated structures.

Rename the @bz format -> @bz_v (specific @bz with df=3) and
@bz_df -> @bz (generic @bz).

Since we modify &msa_bz, re-align its arguments, so the other
structures added in the following commits stay visually aligned.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20211028210843.2120802-8-f4bug@amsat.org>