AMDGPU: Make getSubRegFromChannel a static member of AMDGPURegisterInfo

Summary:
This makes is possible to have R600RegisterInfo and SIRegisterInfo
not inherit from AMDGPURegisterInfo.

Reviewers: arsenm, nhaehnle

Reviewed By: arsenm

Subscribers: kzhuravl, wdng, yaxunl, dstuttard, tpr, llvm-commits, t-tye

Differential Revision: https://reviews.llvm.org/D46280

llvm-svn: 331490
diff --git a/llvm/lib/Target/AMDGPU/R600InstrInfo.cpp b/llvm/lib/Target/AMDGPU/R600InstrInfo.cpp
index 9b8cca1..02e2f40 100644
--- a/llvm/lib/Target/AMDGPU/R600InstrInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/R600InstrInfo.cpp
@@ -72,7 +72,7 @@
 
   if (VectorComponents > 0) {
     for (unsigned I = 0; I < VectorComponents; I++) {
-      unsigned SubRegIndex = RI.getSubRegFromChannel(I);
+      unsigned SubRegIndex = AMDGPURegisterInfo::getSubRegFromChannel(I);
       buildDefaultInstruction(MBB, MI, AMDGPU::MOV,
                               RI.getSubReg(DestReg, SubRegIndex),
                               RI.getSubReg(SrcReg, SubRegIndex))