Decouple Game Driver from preloading graphics driver

Previously, when the Game Driver package name is set, graphics driver preloading
is automatically disabled. Now we'd like to decouple the relation here. So Game
Driver could still work no matter graphics driver is preloaded in Zygote or not.

Bug: 134526352
Test: build, flash and boot.
Change-Id: Id720cc11e3365423dd9b984b7d30a2dbeecb6116