[FastISel] Rename public visible FastISel functions. NFC.

This commit renames the following public FastISel functions:
LowerArguments -> lowerArguments
SelectInstruction -> selectInstruction
TargetSelectInstruction -> fastSelectInstruction
FastLowerArguments -> fastLowerArguments
FastLowerCall -> fastLowerCall
FastLowerIntrinsicCall -> fastLowerIntrinsicCall
FastEmitZExtFromI1 -> fastEmitZExtFromI1
FastEmitBranch -> fastEmitBranch
UpdateValueMap -> updateValueMap
TargetMaterializeConstant -> fastMaterializeConstant
TargetMaterializeAlloca -> fastMaterializeAlloca
TargetMaterializeFloatZero -> fastMaterializeFloatZero
LowerCallTo -> lowerCallTo

Reviewed by Eric

llvm-svn: 217074