rockchip: rk3399: init CPU clock when rkclk_init()

Init the CPU and its buses to speed up the boot time.
Move rkclk_init() to a place after rk3399_configure_cpu has defined
at the same time, or else there will be a warning.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>