Introduce PieceSquareTable[16][64]

Instead of MgPieceSquareTable[16][64] and EgPieceSquareTable[16][64]

This allows to fetch mg and eg values from adjacent words in memory.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/movepick.cpp

@@ -221,7 +221,7 @@ void MovePicker::score_noncaptures() {
           hs += 1000;
 
       // pst based scoring
-      cur->score = hs + pos.pst_delta<Position::MidGame>(piece, from, to);
+      cur->score = hs + pos.pst_delta(piece, from, to).mg();
   }
 }