ARM: dts: rockchip: convert rk3188 to opp-v2

The fact that OPPs specified only on cpu0 work is Linux specific and
normally cpu frequencies should be specified for each cpu core.
To facilitate this without needing to duplicate the frequency table
each time, convert to opp-v2 before adding references to all cores.

Signed-off-by: Heiko Stuebner <heiko.stuebner@bq.com>