drm/amd/powerplay: set soc floor voltage on boot on vega10.

Send the VBIOS bootup VDDC as a SOC floor voltage to SMU
before populating the PPTABLE. After DPM is enabled, This
floor voltage will be removed. This will prevent SMC from
going to Vmin upon receiving PPTable causing a violation.

Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>