drm/amd/include/vg20: adjust VCE_BASE to reuse vce 4.0 header files

Vega20 uses vce 4.1 engine, all the registers have the
same absolute offset with vce 4.0. By adjusting vega20
VCE_BASE, vce 4.1 can reuse vce 4.0 header files.

Signed-off-by: James Zhu <James.Zhu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>