Add a penalty for low mobility pieces

Passed both STC
LLR: 2.96 (-2.94,2.94) [-1.50,4.50]
Total: 81857 W: 14652 L: 14342 D: 52863

and LTC
LLR: 2.97 (-2.94,2.94) [0.00,6.00]
Total: 45400 W: 6999 L: 6697 D: 31704

bench: 7716978
Get rid of an evaluate_pieces() overload

Rewrite and greatly simplify that part of code.

No functional change.
Further simplification in evaluate

No functional change