AMDGPU: Eliminate GPU specific SubtargetFeatures

Inline compatability is determined from the individual feature
bits. These are just sets of the separate features, but will always be
treated as incompatible unless they are specifically ignored.

Defining the ISA version number here in tablegen would be nice, but it
turns out this wasn't actually used.

git-svn-id: 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed