drm/i915/gvt: refactor intel_gvt_io_emulation_ops to be intel_gvt_ops

There are currently 4 methods in intel_gvt_io_emulation_ops
to emulate CFG/MMIO reading/writing for intel vGPU. A possibly
better scope is: add 3 more methods for vgpu create/destroy/reset
respectively, and rename the ops to 'intel_gvt_ops', then pass
it to the MPT module (say the future kvmgt) to use: they are
all methods for external usage.

Signed-off-by: Jike Song <jike.song@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>