Revert "disable GPU OC for now"

This reverts commit 6109d7c9c708cd7361c7e5b1b31f2cf6978202ed.
Revert "finish GPU OC 450 mhz"

This reverts commit 9b3b7caf41d86980c0a6820ddc2192c613e22b36.
Revert "GPU Overclocking: add 450 MHz option"

This reverts commit bf5c1af954958816342493ed655bf9a5506ce1d4.
Revert "finish GPU OC 487.5 mhz"

This reverts commit 80634f142854020309b4ce9eacb537cf972c35eb.