arm64: dts: rockchip: remove wrongly added idle states on rk3368

As reported by Lorenzo, the residency/latency values defined in the
idle-state for rk3368 "make no sense". When introducing them I
simply took the idle-state node from the vendor kernel in error
as I didn't look up if these values were sane in the first place.

Talking to people and determining why they were used in this way
showed that it was meant to make sure the cpu_suspend callback
got initialized which at the 3.10 time was somehow required even
for wfi-based idle handling.

Of course the generic arch_cpu_idle() now does wfi-based idle-handling
already and the rk3368 does not implement any other idle states than
the default WFI, so these wrong idle-states should go away.

Reported-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>