drm/amd/display: dce_hwseq: add DCE6 specific macros,functions

[Why]
DCE6 has no BLND_CONTROL register for Blender HW programming
DCE6 has no BLND_V_UPDATE_LOCK register for Pipe Locking

[How]
Add DCE6 specific macros definitions for HWSEQ registers and masks
DCE6 HWSEQ macros will avoid buiding errors when using DCE6 headers
Add dce60_pipe_control_lock() stub with no op

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>