kevin64 builds using public overlay are currently broken because there is no mali-driver package.

Since it will take a while before all issues with private overlays can be sorted out, it would be nice to make the public overlay builds working.

I have an internal kevin64-full builder setup but it is currently failing in build_packages. If the errors are fixed, it would make it easy to use this builder to know of any regressions.

emerge: there are no ebuilds to satisfy "media-libs/mali-drivers" for /build/kevin64/.
(dependency required by "virtual/opengles-2-r1::baseboard-gru" [ebuild])
(dependency required by "media-gfx/deqp-2018.08.15-r1::chromiumos" [ebuild])
(dependency required by "virtual/target-chromium-os-test-1-r72::chromiumos[ozone,-cros_embedded]" [ebuild])
(dependency required by "virtual/target-os-test-1-r2::chromiumos" [ebuild])
(dependency required by "virtual/target-os-test" [argument])