Add clock driver support for Rockchip RK3576 SoC. Signed-off-by: Elaine Zhang <zhangqing@rock-chips.com> [adapted to mainline u-boot] Signed-off-by: Heiko Stuebner <heiko@sntech.de> Reviewed-by: Jonas Karlman <jonas@kwiboo.se> Reviewed-by: Kever Yang <kever.yang@rock-chips.com>