drm/radeon: fix si_enable_smc_cac() failed issue

Need to set the dte flag on this asic.

Port the fix from amdgpu:
5cb818b8 ("drm/amd/amdgpu: fix si_enable_smc_cac() failed issue")

Reviewed-by: Yong Zhao <yong.zhao@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>