timers: Make 'pinned' a timer property

We want to move the timer migration logic from a 'push' to a 'pull' model.

Under the current 'push' model pinned timers are handled via
a runtime API variant: mod_timer_pinned().

The 'pull' model requires us to store the pinned attribute of a timer
in the timer_list structure itself, as a new TIMER_PINNED bit in
timer->flags.

This flag must be set at initialization time and the timer APIs
recognize the flag.

This patch:

 - Implements the new flag and associated new-style initialization
   methods

 - makes mod_timer() recognize new-style pinned timers,

 - and adds some migration helper facility to allow
   step by step conversion of old-style to new-style
   pinned timers.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Chris Mason <clm@fb.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: George Spelvin <linux@sciencehorizons.net>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Len Brown <lenb@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: rt@linutronix.de
Link: http://lkml.kernel.org/r/20160704094341.049338558@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>