The RK3568 eDP TX controller is almost the same as that of RK3399.
It supports RBR/HBR with 1/2/4 lanes and the max supported resolution
is 2560x1600p60.
The slight difference with RK3399 is the newly added 'apb' reset,
which is just like that of RK3588/RK3576.
Change-Id: Ifd5bc2d8f337b794a6d2983b689d2bd2271d78c2
Signed-off-by: Damon Ding <damon.ding@rock-chips.com>