Make platform_compat discoverable everywhere

The binder's methods are protected by signature
permissions (LOG_COMPAT_CHANGE, READ_COMPAT_CHANGE_CONFIG and
OVERRIDE_COMPAT_CHANGE_CONFIG).

This is a re-landing of https://r.android.com/1210143, which was
reverted due to http://b/142942524. The actual fix was done in
http://ag/10234812.

Bug: 142650523
Test: atest PlatformCompatGatingTest
Change-Id: Ibddac8933ea58d44457a5d80b540347e796ebe71
2 files changed