Revert "arm64: fix infinite stacktrace"

This reverts commit 7e7df71f.

When unwinding out of the IRQ stack and onto the interrupted EL1 stack,
we cannot rely on the frame pointer being strictly increasing, as this
could terminate the backtrace early depending on how the stacks have
been allocated.
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm64/kernel/stacktrace.c

@@ -56,9 +56,6 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
 	frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
 	frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
 
-	if (frame->fp <= fp)
-		return -EINVAL;
-
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 	if (tsk->ret_stack &&
 			(frame->pc == (unsigned long)return_to_handler)) {