drm/amdgpu/swsmu: handle VCN harvesting for VCN SMU setup

Check if VCN instances are harvested when controlling
VCN power gating and setting up VCN clocks.

Fixes: 1b592d00

 ("drm/amdgpu/vcn: remove manual instance setting")
Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1743
Reviewed-and-tested-by: Guchun Chen <guchun.chen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>