arm: Add basic clocks for Rockchip rk3066a SoCs

This adds a basic clock setup for rk3066a SoCs. Only the gates are
set up currently, as the mux and dividers should use the upcoming
generic devicetree bindings.

Clocks whose rates need to be known are supplied by fixed-rate
"dummy"-clocks that provide the correct rate. This is uncritical insofar
that the only bootloader currently in existence for Rockchip devices
is the propietary Rockchip one that always setups the clocks in the
necessary way.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Mike Turquette <mturquette@linaro.org>