ANDROID: GKI: kernel: tick-sched: Add API to get the next wakeup for a CPU

Add get_next_event_cpu to get the next wakeup time for the CPU. This
is used by the sleep driver if it has to query the next wakeup for a
CPU other than the thread that its running on.

Test: make
Bug: 150895657
Signed-off-by: Mahesh Sivasubramanian <msivasub@codeaurora.org>
Change-Id: I0f0347f9648932a55cb64c630694d0a2e290b633
(cherry picked from commit e948653a6a5cb055b5ed692d52817e52f02a1bb1)
[hridya: also added an EXPORT_SYMBOL_GPL(get_next_event_cpu) to make
the symbol available to kernel modules.]
Signed-off-by: Hridya Valsaraju <hridya@google.com>