Echo piece of code from file

You can do this by putting your piece of code in a function and call it where required just like any template tag.

<?php
function the_logo(){   ?>
     <div id="logo">
        <?php if( get_theme_mod( 'mlwd_logo_image') ) : ?>
             <img src="https://wordpress.stackexchange.com/questions/337491/<?php echo esc_url(get_theme_mod("mlwd_logo_image')); ?>" alt="Logo"/>
         <?php else: ?>
             <h1>
                 <a href="<?php echo home_url(); ?>" title="<?php bloginfo('name'); ?>">
                  <?php bloginfo('name'); ?><?php echo $langblog;?>
                 </a>
             </h1>
              <p>
                  <?php bloginfo('description'); ?><?php echo $langblog;?>
              </p>
          <?php endif ?>
      </div>
<?php } ?>

And the header would look like

    <header id="header" class="clear" role="banner">
        <div class="column column-one four-quarter">
            <div class="container clear">
                <?php if( get_theme_mod( 'mlwd_logo_layout', 'insideheader' ) == 'insideheader' ) && get_theme_mod('mlwd_logo_position_y', 'top') :

                    // Piece of code from code.php file
                    the_logo();

                endif ?>
            </div>
        </div>
        <div class="column column-two four-quarter">
            <div class="container clear">
                <?php if( get_theme_mod( 'mlwd_logo_layout', 'insideheader' ) == 'insideheader' ) && get_theme_mod('mlwd_logo_position_y', 'bottom') :

                    // Piece of code from code.php file
                    the_logo();

                endif ?>
            </div>
        </div>
    </header>

I hope this may be helpful,