drm/amdgpu/display: dm/amdgpu: make dp phy debugfs for eDP

drm/amdgpu/display: dm/amdgpu: make dp phy debugfs for eDP

[WHY] dp debugfs file does not exist for eDP under
      /sys/kernel/debug/dri/0/eDP-1. the root is phy debugfs
      is created for dp connector only.
[HOW] for eDP connector, create phy debugfs too.

Signed-off-by: Hersen Wu <hersenxs.wu@amd.com>
Reviewed-by: David Francis <David.Francis@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>