Add channel mask in SoundPool sample.

There may be channel mask information after extracting from files. For
instance, haptic-audio coupled ogg file. In that case, it is preferred
using that channel mask directly to create AudioTrack instead of using
channel count to calculate a channel mask.

Test: manully test with playing with SoundPool.
Bug: 111454766
Change-Id: I0483365cbc1b93587d1c4738b0ed25b2d800718d