Revert "arm64: dts: rockchip: Add basic cpu frequencies for RK3368"

This reverts commit 6f2dea1f

.

Without accurate cpu regulators being set for boards this will wreak havoc
when cpufreq-dt begins to set new frequencies without adjusting the core
frequency.

Additionally the rk3368 has an unsolved issue in that it has two separate
cpu clusters with separate clock lines but only one cpu supply regulator
for both clusters, which causes even more problems.

While it seems that originally only one cluster was supposed to be active
at a time (big or little), talking with real users of the hardware
revealed that having all 8 cores accessible at 1.2GHz max is way more
liked than having 4 cores at 1.5GHz max. Such an approach needs changes
to cpufreq and/or opp though to control the two separate clock lines when
setting both clusters to the same frequencies.

In any case, having the OPPs in the dts at this point in time is
undesireable, so remove them again for now.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>