feat(arch): add the amd64 fp16 packed imm8-control group

Assisted-by: GLM 5.3

arch/arm64_ext.go

@@ -480,6 +480,11 @@ const (
 	// where dest is an opmask register and the immediate's layout is named
 	// by the entry's Imm8 kind.
 	ExtFormAmdMask2Imm
+	// ExtFormAmdVec2Imm is the two-vector form with a control immediate,
+	// VRNDSCALEPH $0x7b, Z5, Z6 style: the immediate leads, the order the
+	// reference listings write it in.  Operands: imm, src, dest, and the
+	// immediate's layout is named by the entry's Imm8 kind.
+	ExtFormAmdVec2Imm
 	// ExtFormAmdMemVec is the memory-load form: VMOVSH X30, 4660(R8) shape,
 	// the manual's xmm1, m16 lines that stand beside the register form.
 	// Operands: mem, dest.
@@ -685,6 +690,8 @@ func (f ExtForm) Arity() int {
 		return 2
 	case ExtFormAmdVec3Imm, ExtFormAmdMask2Imm:
 		return 4
+	case ExtFormAmdVec2Imm:
+		return 3
 	case ExtFormAmdMemVec, ExtFormAmdVecMem:
 		return 2
 	case ExtFormPredicateOne, ExtFormPredicateWrite, ExtFormPredicateCounter:
@@ -808,6 +815,8 @@ func (f ExtForm) String() string {
 		return "immediate, three vectors"
 	case ExtFormAmdMask2Imm:
 		return "immediate, two vectors into an opmask"
+	case ExtFormAmdVec2Imm:
+		return "immediate and two vectors"
 	case ExtFormAmdMemVec:
 		return "memory into a vector"
 	case ExtFormAmdVecMem:
@@ -1057,7 +1066,8 @@ func (in ExtInstr) Encode(ops []ExtOperand) ([]byte, error) {
 	case ExtFormAmdVec3, ExtFormAmdVec2, ExtFormAmdVec2Half, ExtFormAmdMask2,
 		ExtFormAmdVecGprVec, ExtFormAmdGprVec, ExtFormAmdVecGpr,
 		ExtFormAmdVec3Imm, ExtFormAmdMask2Imm, ExtFormAmdMemVec, ExtFormAmdVecMem,
-		ExtFormAmdVec2Wide, ExtFormAmdVec2Quarter, ExtFormAmdVec2ToQuarter:
+		ExtFormAmdVec2Wide, ExtFormAmdVec2Quarter, ExtFormAmdVec2ToQuarter,
+		ExtFormAmdVec2Imm:
 		return in.encodeAmd64(ops)
 	case ExtFormPredicateLogical, ExtFormPredicateSelect:
 		return in.encodePredicateLogical(ops)