Add flag for match content frame rate

Add new Settings.Secure.MATCH_CONTENT_FRAME_RATE to store user's preferred
refresh rate switching type.

Bug: 161776333
Test: 1. adb shell settings put secure match_content_frame_rate [0|1|2]
      2. Verify the setting is correctly propagated:
         adb shell dumpsys display | grep mModeSwitchingType
         adb shell dumpsys SurfaceFlinger | grep allowGroupSwitching
      3. reboot and verify the setting is persisted

Change-Id: I95b3f3f550f3e49f3bc6858185a7f7af1d55a4a7