PM / wakeirq: Convert to SRCU

The wakeirq infrastructure uses RCU to protect the list of wakeirqs. That
breaks the irq bus locking infrastructure, which is allows sleeping
functions to be called so interrupt controllers behind slow busses,
e.g. i2c, can be handled.

The wakeirq functions hold rcu_read_lock and call into irq functions, which
in case of interrupts using the irq bus locking will trigger a
might_sleep() splat.

Convert the wakeirq infrastructure to Sleepable RCU and unbreak it.

Fixes: 4990d4fe (PM / Wakeirq: Add automated device wake IRQ handling)
Reported-by: Brian Norris <briannorris@chromium.org>
Suggested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Tested-by: Brian Norris <briannorris@chromium.org>
Cc: 4.2+ <stable@vger.kernel.org> # 4.2+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>