drm/amd/display: Combine field toggle macro and sequence write macro.

[Why]
field toggle write is actual field sequence write with the same
field name.

[How]
Use REG_UPDATE_SEQ_2 for both sequence write and toggle.
Rename REG_UPDATE_1by1_3 to REG_UPDATE_SEQ_3.

Signed-off-by: Yongqiang Sun <yongqiang.sun@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>