drm/amd/display: Add save/restore PANEL_PWRSEQ_REF_DIV2

drm/amd/display: Add save/restore PANEL_PWRSEQ_REF_DIV2

[why]
DCN31 has this in zstate save/restore sequence.
need for non_zstate supported ASIC

[how]
add this PANEL_PWRSEQ_REF_DIV2 to existing panel_cntl_hw_init structure.

Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Agustin Gutierrez <agustin.gutierrez@amd.com>
Signed-off-by: Charlene Liu <Charlene.Liu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>