drm/amd/display: Remove unused fields from dmub_cmd_update_dirty_rect_data

Drop coasting_vtotal_high and pad from dmub_cmd_update_dirty_rect_data,
since it is not used.

Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Wayne Lin <wayne.lin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>