Make PlatformCompat a Binder class

This allows PlatformCompat to be called from anywhere in the platform.
In follow-up CLs, we'll define permissions for each method and/or
filtering rules to prevent abuse from apps.

Test: m
Bug: 137769727
Change-Id: I19e5fbfefcf59e0b53b197ea8e9e3cb78439b4c4