Audio Description preference updates according to IC reviewing:

1) Update audio description preference summary as the Legal team
   suggestion as b/194376036#comment6
2) Move audio description preference item under "Audio" category as the
   UX team suggestions as b/194376037#comment#9

Preview: https://screenshot.googleplex.com/C24snywjHaRwG3g
Bug: 194376037
Bug: 194376036
Bug: 214634651
Test: local test
Change-Id: Ic72be85120bcf2fd36599cd9aad82b50aad32d04