libhardware: Enable MMAP interface in USB Audio HAL

Allow USB Audio HAL to write using MMAP interface
to support USB Audio AoA feature.
Change-Id: If23d2b618277ab64853fc1d778767a95482bedbf
(cherry picked from commit 1dc50e2b4d2bbac5d39edfd408d011cfaf4cd82b)
(cherry picked from commit bff3e5a4d2d0e61e6c35cfb3ef66be51ae98b3c8)
(cherry picked from commit ba5d429fe4817c48c089d34954daea21f321bf11)