Camera2: Add prepare for output streams

The prepare call asynchronously pre-allocates buffers for a given
output stream, and then fires the onPrepared callback.

Not implemented for Camera2Device or used in Camera2Client.

Change-Id: I1cccdfff846dd6985133c591dbdceed823929ade
diff --git a/services/camera/libcameraservice/device2/Camera2Device.cpp b/services/camera/libcameraservice/device2/Camera2Device.cpp
index 3c5ea9d..f6645f3 100644
--- a/services/camera/libcameraservice/device2/Camera2Device.cpp
+++ b/services/camera/libcameraservice/device2/Camera2Device.cpp
@@ -618,6 +618,12 @@
     return waitUntilDrained();
 }
 
+status_t Camera2Device::prepare(int streamId) {
+    ATRACE_CALL();
+    ALOGE("%s: Camera %d: unimplemented", __FUNCTION__, mId);
+    return NO_INIT;
+}
+
 uint32_t Camera2Device::getDeviceVersion() {
     ATRACE_CALL();
     return mDeviceVersion;