Add UNWINDSVCFRAME to provide the unwind pseudo ops to allow us to unwind

past a trapframe.

Use this macro in exception_exit as it is the function the unwinder enters
as the functions that store the frame setting lr to point to it.

sys/arm/arm/exception.S

@@ -206,7 +206,7 @@ END(address_exception_entry)
  */
 
 ASENTRY_NP(exception_exit)
-	STOP_UNWINDING
+	UNWINDSVCFRAME
 	DO_AST
 	PULLFRAMEFROMSVCANDEXIT
 END(exception_exit)

sys/arm/include/asmacros.h

@@ -206,7 +206,16 @@
         mov     r0, r0;	  		/* NOP for previous instruction */ \
 	add	sp, sp, #(4*15);	/* Adjust the stack pointer */	   \
 	ldmia	sp, {sp, lr, pc}^	/* Restore lr and exit */
-#endif 
+#endif
+#if defined(__ARM_EABI__)
+#define	UNWINDSVCFRAME							   \
+	.save {r13-r15};		/* Restore sp, lr, pc */	   \
+	.pad #(2*4);			/* Skip user sp and lr */	   \
+	.save {r0-r12};			/* Restore r0-r12 */		   \
+	.pad #(4)			/* Skip spsr */
+#else
+#define	UNWINDSVCFRAME
+#endif
 
 #define	DATA(name) \
 	.data ; \