CHROMIUM: arm64: dts: rockchip: set higher voltages for gpu

This bumps up 25mv for GPU 400M and 594M.

BUG=chrome-os-partner:60508
TEST=emerge

Change-Id: I76b3ab99cf13a220b6093fec20b384b1f45f810a
Signed-off-by: Shunqian Zheng <zhengsq@rock-chips.com>
Reviewed-on: https://chromium-review.googlesource.com/415771
Commit-Ready: Douglas Anderson <dianders@chromium.org>
Tested-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
(cherry picked from commit fe97b0e69ca7af05f93ce02e0694070cc690384f)
Reviewed-on: https://chromium-review.googlesource.com/416352