drm/i915/gvt: Introduce basic vGPU life cycle management

A vGPU represents a virtual Intel GEN hardware, which consists following
virtual resources:

- Configuration space (virtualized)
- HW registers (virtualized)
- GGTT memory space (partitioned)
- GPU page table (shadowed)
- Fence registers (partitioned)

* virtualized: fully emulated by GVT-g.
* partitioned: Only a part of the HW resource is allowed to be accessed
by VM.
* shadowed: Resource needs to be translated and shadowed before getting
applied into HW.

This patch introduces vGPU life cycle management framework, which is
responsible for creating/destroying a vGPU and preparing/free resources
related to a vGPU.

Signed-off-by: Zhi Wang <zhi.a.wang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>