[CostModel][AMDGPU] Fix intrinsics costs estimations.

1. Fixed costs inconsistency for llvm.fma.vXf16 instinsiscs.
2. Added tests for llvm.sadd.sat, llvm.ssub.sat, llvm.uadd.sat, llvm.usub.sat
   intrisics since they have special processing in cost model.
3. Minor intrisics' costs tests updat and refinement.

Reviewed By: rampitec

Differential Revision: https://reviews.llvm.org/D115385