Exempting time-tick from device-idle

The device screen may be on and the clock may be visible while the
device is in idle mode. We should allow time_tick to flow normally in
such cases.

Test: Manual inspection of flags from the output of
adb shell dumpsys alarm
should show flag value of 0x9 for the alarm TIME_TICK
when time_tick_allowed_while_idle is true, and 0x1 when
time_tick_allowed_while_idle is false.

Bug: 163270237
Change-Id: I4ca345f5cb14c317462d9a5b0ec9bac9f9f69b41