target/arm: Rename do_zzz_fp to gen_gvec_ool_fpst_arg_zzz

Rename the function to match gen_gvec_ool_arg_zzz,
and move to be adjacent.  Split out gen_gvec_fpst_zzz
as a helper while we're at it.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220527181907.189259-86-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>