drm/amd/powerplay: add interface to set min dcef deep sleep (v2)

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>