Add "PowerVR" to GT7600, GT7800, and GX6450 (iOS jobs).
Add model number G6430 to NexusPlayer.
Change-Id: Id0beb9e25ac793378fcd353836a43b2ea9db1aef
Reviewed-on: https://skia-review.googlesource.com/148668
Auto-Submit: Ben Wagner <benjaminwagner@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
