fix(loong64): FP immediates through R30 and unsigned branch forms

Assisted-by: GLM 5.3

arch/arch.go

@@ -55,6 +55,7 @@ const (
 	Mask                    // AVX-512 mask register (K)
 	Float                   // arm64 floating-point register (F)
 	VecARM                  // arm64 SIMD/vector register (V)
+	VecSIMD                 // architecture-neutral SIMD/vector register (LoongArch LSX/LASX)
 	Special                 // architecture-special register
 )
 
@@ -73,6 +74,8 @@ func (c RegClass) String() string {
 		return "float"
 	case VecARM:
 		return "vector (arm64)"
+	case VecSIMD:
+		return "vector"
 	case Special:
 		return "special"
 	default:

arch/loong64.go

@@ -31,10 +31,10 @@ func loong64Registers() []Register {
 		add(fmt.Sprintf("F%d", i), Float, "floating-point register")
 	}
 	for i := 0; i <= 31; i++ {
-		add(fmt.Sprintf("V%d", i), VecARM, "LSX 128-bit vector register")
+		add(fmt.Sprintf("V%d", i), VecSIMD, "LSX 128-bit vector register")
 	}
 	for i := 0; i <= 31; i++ {
-		add(fmt.Sprintf("X%d", i), VecARM, "LASX 256-bit vector register")
+		add(fmt.Sprintf("X%d", i), VecSIMD, "LASX 256-bit vector register")
 	}
 	return regs
 }