The broadcast code shuts down the local clock event unconditionally
even if no broadcast device is installed or if the broadcast device is
hrtimer based.

Add proper sanity checks.

[ Split out from a larger combo patch ]
Reported-and-tested-by: NSudeep Holla <sudeep.holla@arm.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Cc: Suzuki Poulose <Suzuki.Poulose@arm.com>
Cc: Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>
Cc: Catalin Marinas <Catalin.Marinas@arm.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1507070929360.3916@nanos