[RISCV] isel (shl (and X, C2), C) -> (slli (srliw X, C3), C3+C).

where C2 has 32 leading zeros and C3 trailing zeros.

When the shl is used by an add C is 1,2 or 3, we end up matching
(add (shl X, C), Y) first. This leaves an and with a constant that
is harder to materialize.