This patch adds interface to set min dcef deep sleep for smu.
It's to set min deep sleep dce fclk with bootup value from vbios via
SetMinDeepSleepDcefclk MSG.

v2: add detailed info to describe this function
Signed-off-by: Huang Rui <ray.huang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>