tcg/i386: Merge tcg_out_movcond{32,64}

Pass a rexw parameter instead of duplicating the functions.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>