drm/amd/display: Rename dml2 to dml2_0 folder

drm/amd/display: Rename dml2 to dml2_0 folder

[Why]
dml2 folder contains all logic for all versions of DML2
This is currently DML2.0 and DML2.1.
Rename dml2 to dml2_0 folder to reflect this better (dml2_0
for DML2.0).

[How]
Rename dml2 to dml2_0 folder and update dml2 references to
use dml2_0 folder.

Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Signed-off-by: Austin Zheng <Austin.Zheng@amd.com>
Signed-off-by: waynelin <Wayne.Lin@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>