AMDGPU: Cleanup subtarget features

Try to avoid mutually exclusive features. Don't use
a real default GPU, and use a fake "generic". The goal
is to make it easier to see which set of features are
incompatible between feature strings.

Most of the test changes are due to random scheduling changes
from not having a default fullspeed model.

llvm-svn: 310258
diff --git a/llvm/test/CodeGen/AMDGPU/vector-extract-insert.ll b/llvm/test/CodeGen/AMDGPU/vector-extract-insert.ll
index ab2bfcf..e3027d0 100644
--- a/llvm/test/CodeGen/AMDGPU/vector-extract-insert.ll
+++ b/llvm/test/CodeGen/AMDGPU/vector-extract-insert.ll
@@ -1,4 +1,4 @@
-; RUN: llc -march=amdgcn -verify-machineinstrs < %s | FileCheck -check-prefix=GCN %s
+; RUN: llc -march=amdgcn -mcpu=tahiti -verify-machineinstrs < %s | FileCheck -check-prefix=GCN %s
 
 ; Test that when extracting the same unknown vector index from an
 ; insertelement the dynamic indexing is folded away.
@@ -81,4 +81,4 @@
 }
 
 attributes #0 = { nounwind readnone }
-attributes #1 = { nounwind }
\ No newline at end of file
+attributes #1 = { nounwind }