Revert to byTypeBB[0] storing occupied squares

As it was in Glaurung times. Also rearranged order
so that byTypeBB[0] is accessed before byTypeBB[x]
to be more cache friendly. It seems there is even
a small speedup.

No functional change.

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

src/types.h

@@ -200,7 +200,7 @@ enum Value {
 };
 
 enum PieceType {
-  NO_PIECE_TYPE = 0,
+  NO_PIECE_TYPE = 0, ALL_PIECES = 0,
   PAWN = 1, KNIGHT = 2, BISHOP = 3, ROOK = 4, QUEEN = 5, KING = 6
 };