arm64: remove __exception annotations

Since commit 73267498 ("arm64: unwind: reference pt_regs via embedded
stack frame") arm64 has has not used the __exception annotation to dump
the pt_regs during stack tracing. in_exception_text() has no callers.

This annotation is only used to blacklist kprobes, it means the same as
__kprobes.

Section annotations like this require the functions to be grouped
together between the start/end markers, and placed according to
the linker script. For kprobes we also have NOKPROBE_SYMBOL() which
logs the symbol address in a section that kprobes parses and
blacklists at boot.
Using NOKPROBE_SYMBOL() instead allows the linker to place these
functions somewhere sensible, and saves us from having an
arm64 specific spelling of __kprobes.

Signed-off-by: James Morse <james.morse@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>

---
(__exception_irq_entry means no-kprobes and optionally in a section
 ftrace can use to pretty-print interrupt handler boundaries)