Update Documentation and name for EPOCH_TIME to ANDROID_EPOCH_TIME.

This is a change in behaviour for ANDROID_EPOCH_TIME property to align it with a future revisions.

This change was submitted to VHAL HIDL in http://ag/15618006.

Bug: 157504928
Bug: 202379958
Test: build using `make -j96 android.hardware.automotive.vehicle-V1-java`
Test: atest VehicleHalDefaultConfigTest

Change-Id: I464b9215f4bdcbbf53c1239b6d38f9940248b5cf