arch-arm: Removing Serializing flag from ISB

ISB Serializing behaviour is guaranteed by IsSquashAfter,
which is inherently serializing; when instruction is commited,
consecutive instructions are flushed and refetched.

Change-Id: I05e61b4cf9f01113d95b1502c996d04cbd69b759
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/5701
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

src/arch/arm/isa/insts/misc.isa

@@ -1154,7 +1154,7 @@ let {{
     isbIop = InstObjParams("isb", "Isb", "ImmOp",
                              {"code": isbCode,
                                "predicate_test": predicateTest},
-                                ['IsSerializeAfter', 'IsSquashAfter'])
+                                ['IsSquashAfter'])
     header_output += ImmOpDeclare.subst(isbIop)
     decoder_output += ImmOpConstructor.subst(isbIop)
     exec_output += PredOpExecute.subst(isbIop)

src/arch/arm/isa/insts/misc64.isa

@@ -140,7 +140,7 @@ let {{
     exec_output += BasicExecute.subst(unknown64Iop)
 
     isbIop = InstObjParams("isb", "Isb64", "ArmStaticInst", "",
-                           ['IsSerializeAfter', 'IsSquashAfter'])
+                           ['IsSquashAfter'])
     header_output += BasicDeclare.subst(isbIop)
     decoder_output += BasicConstructor64.subst(isbIop)
     exec_output += BasicExecute.subst(isbIop)