timer: Add a global deferrable timer

Add a global deferrable timer in addition to the per-cpu deferrable timer
to allow deferrable timers without the TIMER_PINNED flag to run
on any active CPU.

Change-Id: I8e6b77cef972589912ad18f324c46c936fbbb96f
Signed-off-by: Kyle Yan <kyan@codeaurora.org>
Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>