[RISCV] Propagate VL from segment store in VLoptimizer

[topperc]

If an arithmetic operation is consumed by a segment store, we should be able to propagate the VL from the segment store to the arithmetic operation.

CC: @lukel97 @preames

[llvmbot]

@llvm/issue-subscribers-backend-risc-v

Author: Craig Topper (topperc)

If an arithmetic operation is consumed by a segment store, we should be able to propagate the VL from the segment store to the arithmetic operation.

CC: @lukel97 @preames