NuPlayer: update timestamp handling

Use getTimestamp WOULD_BLOCK error return code to clean up
initial playback/start timestamp handling.

Account for pause time and seeks.
Only send notification from driver when the media time changes.

Bug: 14659809
Bug: 17428188
Change-Id: I051bb5e2dd4fd5990474f8fb635615ad8d18eb2c
3 files changed