[AMDGPU] Ensure trig range reduction only used for subtargets that require it

Summary:
GFX9 and above support sin/cos instructions with a greater range and thus don't
require a fract instruction prior to invocation.

Added a subtarget feature to reflect this and added code to take advantage of
expanded range on GFX9+

Also updated the tests to check correct behaviour

Subscribers: arsenm, kzhuravl, jvesely, wdng, nhaehnle, yaxunl, tpr, t-tye, llvm-commits

Differential Revision: https://reviews.llvm.org/D51933

Change-Id: I1c1f1d3726a5ae32116646ca5cfa1ab4ef69e5b0
llvm-svn: 342222