Fix compiler error with when Zicsr is disabled

When using 'make ENABLE_Zicsr=0', the following error is observed:

src/emulate.c:561:10: error: ‘rv_insn_csrrw’ undeclared (first use in this function); did you mean ‘rv_insn_csrai’?
  561 |     case rv_insn_csrrw:
      |          ^~~~~~~~~~~~~
      |          rv_insn_csrai

The error occurs because CSR instruction enums are only defined when
the Zicsr extension is enabled. By adding the feature guard, we ensure
the switch cases are only compiled when the required instruction
definitions are available.

Author: eleanorLYJ

src/emulate.c

@@ -558,7 +558,9 @@ FORCE_INLINE bool insn_is_unconditional_branch(uint8_t opcode)
     case rv_insn_jal:
     case rv_insn_jalr:
     case rv_insn_mret:
+#if RV32_HAS(Zicsr)
     case rv_insn_csrrw:
+#endif
 #if RV32_HAS(SYSTEM)
     case rv_insn_sret:
 #endif