arm64-asm.c: remove dead operand type definitions

OPT_VREG, OPT_IM12, OPT_SHIFT, and OPT_REGSET were defined in the enum
and as OP_* bit masks but never used by any parsing function or
instruction handler in arm64-asm.c.

These appear to be artifacts copied from other assembler implementations
(arm-asm.c uses OP_VREG32/OP_VREG64/OP_REGSET32, riscv64-asm.c uses
OP_IM12S) but were never integrated into the ARM64 operand parsing logic.

Removing these unused definitions:
- Eliminates confusion for developers
- Reduces code clutter
- Makes the actual operand types (OPT_REG, OPT_IM, OPT_ADDR, OPT_COND)
  clearer

arm64-asm.c

@@ -36,22 +36,15 @@ ST_FUNC void gen_le32(int c);
 /* Operand types */
 enum {
     OPT_REG,
-    OPT_VREG,
     OPT_IM,
-    OPT_IM12,
     OPT_ADDR,
     OPT_COND,
-    OPT_SHIFT,
-    OPT_REGSET,
 };
 
 #define OP_REG     (1 << OPT_REG)
-#define OP_VREG    (1 << OPT_VREG)
 #define OP_IM      (1 << OPT_IM)
 #define OP_ADDR    (1 << OPT_ADDR)
 #define OP_COND    (1 << OPT_COND)
-#define OP_SHIFT   (1 << OPT_SHIFT)
-#define OP_REGSET  (1 << OPT_REGSET)
 
 typedef struct Operand {
     uint32_t type;