Allow mediaserver to access fd allocated by hal_graphics_composer

Bug:  37713584
Test: With GtsMediaTestCases.apk installed, try:
      adb shell am instrument -w
      -e class 'com.google.android.media.gts.MediaPlayerTest#testLLAMA_H264_BASELINE_240P_800_DOWNLOADED_V0_SYNC'
      'com.google.android.media.gts/android.support.test.runner.AndroidJUnitRunner'

Change-Id: Icc2066e9d9bbc5c020b6d694e9627487771ef35e