Add clock driver for RK3506.
Imported from vendor U-Boot linux-6.1-stan-rkr6 tag with minor
adjustments and fixes for mainline.
Signed-off-by: Finley Xiao <finley.xiao@rock-chips.com>
Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>