[Why]
SOC_BOUNDING_BOX_VALID is unused and not required for dcn21.

[How]
Remove it.
Signed-off-by: NRoman Li <Roman.Li@amd.com>
Reviewed-by: NBhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Acked-by: NQingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>