Move "volume" commands over to Binder.

Keep the old socket-based commands intact for awhile so we can
rapidly disable this change using the ENABLE_BINDER feature flag.

Define constants in AIDL to keep Java and C++ in sync.

Test: cts-tradefed run commandAndExit cts-dev -m CtsAppSecurityHostTestCases -t android.appsecurity.cts.ExternalStorageHostTest
Test: cts-tradefed run commandAndExit cts-dev --abi armeabi-v7a -m CtsAppSecurityHostTestCases -t android.appsecurity.cts.AdoptableHostTest
Bug: 13758960
Change-Id: Ie0d917c921b0b826e6bdf55a5d678b247ef352a6