Add default alarm tone.

Alarms were removed previously to reduce the space required for the
system image. But we still need a default one for the RingtoneManager
tests.

Bug: 110449143
Test: cts -m CtsMediaTestCases -t android.media.cts.RingtoneManagerTest#testSetType
Change-Id: Iee91156059f3440fbb6a0b28765dd3bb0b997cf5
(cherry picked from commit ecf1bfc3e4109d6f43b3fe4d27bc8035fbd462d8)