R600/SI: Temporary fix for f64 fneg

This should be a source modifier, but this unblocks
most of my math patches.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211181 91177308-0d34-0410-b5e6-96231b3b80d8
R600: Custom lower f64 frint for pre-CI

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211182 91177308-0d34-0410-b5e6-96231b3b80d8
R600: Implement f64 ftrunc, ffloor and fceil.

CI has instructions for these, so this fixes them for older hardware.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211183 91177308-0d34-0410-b5e6-96231b3b80d8