drm/amd/display: Add SMU interface to get UMC count for dcn401

drm/amd/display: Add SMU interface to get UMC count for dcn401

[WHY&HOW]
BIOS table will not always contain accurate UMC channel info when
harvesting is enabled, so get the correct info from SMU.

Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Signed-off-by: Dillon Varone <dillon.varone@amd.com>
Signed-off-by: Tom Chung <chiahsuan.chung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>