Block GPU on dequeue fence only if it has not signalled already

When Vulkan pipeline dequeues next frame at the beginning of
DrawFrame, the dequeue fence has been signalled in most cases.
This CL avoids additional work and saves about 0.3ms per frame.
There is no need to create VkSemaphore and commit an empty command
buffer to the queue if the fence has already signalled.

Bug: 128998567
Test: Ran systrace on SelfieCity and observed better performance
Change-Id: I3532b785fae90308d922a29f1698f5dbcbd79079