aarch64: discard async aborts on entering debug state

recommended for Corte-A8 cores, not sure if necessary
for ARMv8 based cores as well.

Change-Id: Ibcb36170c5fac6a6b132de17f734c70a56919f9b
Signed-off-by: Matthias Welwarsky <matthias.welwarsky@sysgo.com>

src/target/armv8_opcodes.h

@@ -135,6 +135,8 @@
 
 #define ARMV8_DSB_SY				0xd5033F9F
 #define ARMV8_DSB_SY_T1				0xf3bf8f4f
+#define ARMV8_ISB				0xd5033fdf
+#define ARMV8_ISB_SY_T1				0xf3bf8f6f
 
 #define ARMV8_MRS(System, Rt)	(0xd5300000 | ((System) << 5) | (Rt))
 /* ARM V8 Move to system register. */
@@ -173,6 +175,7 @@ enum armv8_opcode {
 	ARMV8_OPC_DSB_SY,
 	ARMV8_OPC_DCPS,
 	ARMV8_OPC_DRPS,
+	ARMV8_OPC_ISB_SY,
 	ARMV8_OPC_NUM,
 };