Update piece counts on all (game-level) promotions

Update piece counts on all (game-level) promotions

The piece count was only updated for entered moves in case of promotion
to royalty (which only occurs in Spartan, as underpromotion, so Fairy-Max
would never do it by itself). This is now moved to the 'first-floor exit',
where it is done for any game move and any piece type, so that piece count
pl[] are completely reliable in the root. (Preparing their use for
determination of mating potential.)