drm/amd/display: Check if set_blank_data_double_buffer exists before call

Not all ASIC types have this function implemented - check before
calling.

Signed-off-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Reviewed-by: Julian Parkin <jparkin@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>