[AMDGPU] Take advantage of VOP3 literals in convertToThreeAddress

[foad]

Summary

This improves a corner case where v_fmac can be converted to v_fma on
GFX10+ even if it has a literal operand.

llvm/lib/Target/AMDGPU/SIInstrInfo.cpp

if (Src0Literal || getFoldableImm(Src0, Imm, &DefMI)) {
         if (DefMI)
           killDef();
         return MIB;
       }
     }
   }
 
   // VOP2 mac/fmac with a literal operand cannot be converted to VOP3 mad/fma
-  // because VOP3 does not allow a literal operand.
-  // TODO: Remove this restriction for GFX10.
-  if (Src0Literal)
+  // if VOP3 does not allow a literal operand.
+  if (Src0Literal && !ST.hasVOP3Literal())
     return nullptr;
 
   unsigned NewOpc = IsFMA ? IsF16 ? AMDGPU::V_FMA_F16_gfx9_e64
                                   : IsF64 ? AMDGPU::V_FMA_F64_e64
                                           : IsLegacy
                                                 ? AMDGPU::V_FMA_LEGACY_F32_e64
                                                 : AMDGPU::V_FMA_F32_e64
                           : IsF16 ? AMDGPU::V_MAD_F16_e64

llvm/test/CodeGen/AMDGPU/llvm.amdgcn.fma.legacy.ll

 ; GCN-NEXT:    s_waitcnt_vscnt null, 0x0
 ; GCN-NEXT:    v_fmac_legacy_f32_e32 v1, 0x41200000, v0
 ; GCN-NEXT:    v_mov_b32_e32 v0, v1
 ; GCN-NEXT:    s_setpc_b64 s[30:31]
 ; GFX10-LABEL: v_fma_imm:
 ; GFX10:       ; %bb.0:
 ; GFX10-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
 ; GFX10-NEXT:    s_waitcnt_vscnt null, 0x0
-; GFX10-NEXT:    v_fmac_legacy_f32_e32 v1, 0x41200000, v0
-; GFX10-NEXT:    v_mov_b32_e32 v0, v1
+; GFX10-NEXT:    v_fma_legacy_f32 v0, 0x41200000, v0, v1
 ; GFX10-NEXT:    s_setpc_b64 s[30:31]
 ;
 ; GFX11-LABEL: v_fma_imm:
 ; GFX11:       ; %bb.0:
 ; GFX11-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
 ; GFX11-NEXT:    s_waitcnt_vscnt null, 0x0
-; GFX11-NEXT:    v_fmac_dx9_zero_f32_e32 v1, 0x41200000, v0
-; GFX11-NEXT:    s_delay_alu instid0(VALU_DEP_1)
-; GFX11-NEXT:    v_mov_b32_e32 v0, v1
+; GFX11-NEXT:    v_fma_dx9_zero_f32 v0, 0x41200000, v0, v1
 ; GFX11-NEXT:    s_setpc_b64 s[30:31]
   %fma = call float @llvm.amdgcn.fma.legacy(float %a, float 10.0, float %c)
   ret float %fma
 }
 
 define float @v_fabs_fma(float %a, float %b, float %c)  {
 ; GFX10-LABEL: v_fabs_fma:
 ; GFX10:       ; %bb.0: