timer: Update code that migrates timers and hrtimers during isolation

__migrate_timers() can be called from both hotplug and isolation
contexts. When called from the isolation context, we might sometimes
encounter running timers. This is OK since the currently running or
just expired timers are off of the timer wheel and so everything else
can be migrated off.

In the case of hrtimers, we must wait until all callbacks have finished.
However, a udelay is important while waiting to allow for store-exclusive
fairness when run_hrtimer is attempting to grab the hrtimer base lock.

Change-Id: I037373930fe709eeeea5a28df803531a59132c76
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>
[markivx: Forward port to 4.14, fix header include conflict]
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>
[satyap@codeaurora.org: Port to 4.19 and fix merge conflict]
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>