drm/rockchip: cdn-dp: remove the DP phy switch

There are 2 Type-c PHYs in RK3399, but only one DP controller. Hence
only one PHY can connect to DP controller at one time, the other should
be disconnected. The GRF_SOC_CON26 register has a switch bit to do it,
set this bit means enable PHY 1, clear this bit means enable PHY 0.

If the board has 2 Type-C ports, the DP driver get the phy id from
devm_of_phy_get_by_index, and then control this switch according to
this id. But some others board only has one Type-C port, it may be PHY 0
or PHY 1. The dts node id can not tell us the correct PHY id. Hence move
this switch to PHY driver, the PHY driver can distinguish between PHY 0
and PHY 1, and then write the correct register bit.

Signed-off-by: Chris Zhong <zyw@rock-chips.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
[The phy-changes are in the phy-tree now and the cdn-dp wasn't
 enabled at all so far, so this change can go through drm-misc
 alone without causing issues when testing drm-misc]
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20180216120956.19034-6-enric.balletbo@collabora.com