[RISCV] Correct costs for vector ceil/floor/trunc/round

Add vector costs for ceil/floor/trunc/round. As can be seen in the tests, the prior default costs were a significant under estimate of the actual code generated.

These costs are computed by simply generating code with the current backend, and then counting the number of instructions. I discount one vsetvli, and ignore the return.

Differential Revision: https://reviews.llvm.org/D131967