x86/entry: Clarify irq_{enter,exit}_rcu()

x86/entry: Clarify irq_{enter,exit}_rcu()

Because:

  irq_enter_rcu() includes lockdep_hardirq_enter()
  irq_exit_rcu() does *NOT* include lockdep_hardirq_exit()

Which resulted in two 'stray' lockdep_hardirq_exit() calls in
idtentry.h, and me spending a long time trying to find the matching
enter calls.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]