drm/amdgpu/virt: rename fieldes of virtualization structure

Use acronym to rename fields to make easy to spell out.

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