ANDROID: GKI: kernel: tick-sched: Move wake callback registration code

The code to register a wakeup callback exists outside of the #ifdef
CONFIG_HIGH_RES_TIMERS which actually uses it, causing compilation errors.
Move it inside the block, where it belongs.

Bug: 162654685
Fixes: 4c3d3d24 ("kernel: tick-sched: Add an API for wakeup callbacks")
Change-Id: I3876481c71d63f4cc655280bdd183024b70897c8
Signed-off-by: J. Avila <elavila@google.com>