Update documentation for android.frameworks.cameraservice.device@2.0.

Explicitly mention that submitRequestList method and onResultReceived callback must be called
serially, incase the client/framework opts to use fmq to send metadata.

Bug: 110364143

Test: mm -j64

Change-Id: I4fc9a891eaad6f1cf9f9ef14a7b399a64cb3163c
Signed-off-by: Jayant Chowdhary <jchowdhary@google.com>