libbinder_ndk: service notifications

Hey - this API looks shiny. You probably want to use
waitForService instead - because 99% of the time, guaranteeing the
code works is more important than controlling the boot order. For
the cases we really really really need to be impatient, here we
go! :)

Bug: 232878913
Test: libbinder_ndk_unit_test
Change-Id: Iae090a8cc48e968faec1d75cf304e2995b9553e0