[RISCV] Remove lmuls argument in Sched class

The original intention is adding a list of SchedWrites (which is a
default argument of ReadAdvance) to LMULReadAdvance, but it may not
be practical that there are two default arguments in one class. So
we add variants that are intended for widening and narrowing
instructions with postfix "W" and remove lmuls argument.

Reviewed By: michaelmaitland

Differential Revision: https://reviews.llvm.org/D138640