drm/amdgpu/vce2: fix vce bar programming

Program the VCE BAR and offsets properly.  The current code
was carried over from a limitation from older VCE versions.

Reviewed-by: Junwei Zhang <Jerry.Zhang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>