phy: rockchip: snps-pcie3: Add bifurcation support for RK3568

Configure aggregation or bifurcation mode on RK3568 based on the value
of data-lanes property.

Code imported almost 1:1 from mainline linux driver.

Fixes: 6ec62b6c ("phy: rockchip: Add Rockchip Synopsys PCIe 3.0 PHY")
Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>