Move sync_wait for screen capture to client

Free up time from the SF's main thread by moving the fence waiting
to the client.

Test: Observe systrace of region sample thread
Test: adb shell screencap
Test: Recents takes the screenshot
Test: Rotate device
Test: Volume + power down for screenshot
Bug: 178649983
Change-Id: Ice70b8d2b95928a5adce19dbd1d91e73d8529f54