eclass/cros-kernel: Enable Analogix DP bridge in rockchip64_defconfig

The display on Kevin is routed via an Analogix DP bridge built into
the SoC. Add necessary config options to rockchip64_defconfig.

BUG=chromium:907715
TEST=Display lights up with upstream kernel on a kevin

Change-Id: I464ffc2b766641ef70e98a7481ae81a0113b2166
Reviewed-on: https://chromium-review.googlesource.com/1351313
Commit-Ready: Douglas Anderson <dianders@chromium.org>
Tested-by: Tomasz Figa <tfiga@chromium.org>
Reviewed-by: Kristian H. Kristensen <hoegsberg@chromium.org>
1 file changed