clk: rockchip: rk3399: Add dummy support for ACLK_VDU clock

clk: rockchip: rk3399: Add dummy support for ACLK_VDU clock

rk3399.dtsi from linux v5.19 and newer try to set VDU clock rate to
400 MHz using an assigned-clock-rates prop of the CRU node.

U-Boot does not use or need this clock so add dummy support for getting
and setting ACLK_VDU clock rate to allow CRU driver to be loaded with an
updated rk3399.dtsi.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>