Merge amdgpu_dm_display_resume function into dm_resume,
as it is not called anywhere else anymore.

Initially the call was broken down into 2 functions for cursor corruption
issue. Now the issue is not visible, hence the dm_resume will perform
dm_display_resume in it.
Signed-off-by: Mikita Lipski <mikita.lipski@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>