Use new API to query mmap support on Android device.

[flamme]

With devices moving to AIDL HAL, they are reporting mmap capabilities via new HAL API. In that case, they may deprecate the old system properties that was used to report mmap capabilities. OboeTester should use the new API to query mmap policy so that it can show correctly from the UI about if mmap can be used or not. Oboe should also wrap the API so that apps can use it easily.