Change Android version to v8.0.0

Change PLATFORM_VERSION.OPD1 to v8.0.0.  This is a temporary
change until we get a new KeyMaster that can handle going from
8.0.1 -> 8.0.0.  At that point we will change PLATFORM_VERSION
to 8.0.0.

Test: Check: Settings > System > About phone > Android version.
Also verified that update from 8.0.1 to v8.0.0 works (i.e. device
boots and shows new Android Version).
Bug: 64130669
Merged-In: I7894321971c0b696594deb064ebed3f43cf7c8d1
Change-Id: Ibb8fbb123a74196f57f649d0c22f58beefaf6d06