drm/amd/display: dce60_hw_sequencer: add DCE6 specific functions (v2)

[Why]
DCE6 has no bottom_pipe and no Blender HW
DCE6 needs 'blank_target' set to false in order to turn on the display
DCE6 has a specific dce60_pipe_control_lock() fuction that is a no op

[How]
Add DCE6 specific functions with needed private dce60_* dependent fuctions
Comment DCE6 specific CTRC program visibility implementation
Fix a typo in the initial header includes comment 's/DCE8/DCE6/g'
Use dce60_apply_ctx_for_surface() in dce60_hw_sequencer_construct
Use dce60_pipe_control_lock() in dce60_hw_sequencer_construct

v2: add missing return type (Alex)
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Mauro Rossi <issor.oruam@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>