AMDGPU: Define FP_FAST_FMA{F} macros for amdgcn

- Expand GK_*s (i.e. GFX6 -> GFX600, GFX601, etc.)
  - This allows us to choose features correctly in some cases (for example, fast fmaf is available on gfx600, but not gfx601)
- Move HasFMAF, HasFP64, HasLDEXPF to GPUInfo tables
- Add HasFastFMA, HasFastFMAF to GPUInfo tables
- Add missing tests

llvm-svn: 326254