[AMDGPU] Use subtarget feature for v_lshl_add_u64 pattern. NFC.

Following on from llvm#133723, use the new subtarget feature for the
selection pattern as well as for the instruction definition.

Author: jayfoad

llvm/lib/Target/AMDGPU/VOP3Instructions.td

@@ -806,7 +806,7 @@ def : GCNPat<
  (DivergentBinFrag<mul> i32:$src0, IsPow2Plus1:$src1),
  (V_LSHL_ADD_U32_e64 i32:$src0, (i32 (Log2_32 imm:$src1)), i32:$src0)>;
 
-let SubtargetPredicate = isGFX940Plus in
+let SubtargetPredicate = HasLshlAddU64Inst in
 def : GCNPat<
   (ThreeOpFrag<shl_0_to_4, add> i64:$src0, i32:$src1, i64:$src2),
   (V_LSHL_ADD_U64_e64 VSrc_b64:$src0, VSrc_b32:$src1, VSrc_b64:$src2)