TIF: fix a race condition when TvInputManager is initialized

Currently, TvInputManagerService notifies the initial state of each
input via TvInputManagetCallback#onInputStateChanged after TvInputManager
is created. However, this is racy because the client may call methods
like getTvInputState() before the initialization.

This patch makes sure that the client gets the control when the initialization
finishes completely.

Bug: 18419452
Change-Id: I5d8141c20984013e68f2809120710c670557c9ad