kgdb: fix several kgdb regressions

kgdb core fixes:
- Check to see that mm->mmap_cache is not null before calling
  flush_cache_range(), else on arch=ARM it will cause a fatal
  fault.

- Breakpoints should only be restored if they are in the BP_ACTIVE
  state.

- Fix a typo in comments to "kgdb_register_io_module"

x86 kgdb fixes:
- Fix the x86 arch handler such that on a kill or detach that the
  appropriate cleanup on the single stepping flags gets run.

- Add in the DIE_NMIWATCHDOG call for x86_64

- Touch the nmi watchdog before returning the system to normal
  operation after performing any kind of kgdb operation, else
  the possibility exists to trigger the watchdog.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/kernel/traps_64.c b/arch/x86/kernel/traps_64.c
index 055b165..4e07332 100644
--- a/arch/x86/kernel/traps_64.c
+++ b/arch/x86/kernel/traps_64.c
@@ -600,8 +600,13 @@
 
 void __kprobes die_nmi(char *str, struct pt_regs *regs, int do_panic)
 {
-	unsigned long flags = oops_begin();
+	unsigned long flags;
 
+	if (notify_die(DIE_NMIWATCHDOG, str, regs, 0, 2, SIGINT) ==
+	    NOTIFY_STOP)
+		return;
+
+	flags = oops_begin();
 	/*
 	 * We are in trouble anyway, lets at least try
 	 * to get a message out.