drm/i915/gvt: Stop initializing pvinfo through reading mmio

The region of pvinfo is reserved for communication between a VMM and
the GPU driver executing on a virtual machine. HW doesn't have any
backing mmio store support for the pvinfo region, thus accessing to
this range through MMIO read/write from host side is forbidden which
is regarded as unclaimed register access.

This patch leaves pvinfo range be initialized with zero.

Signed-off-by: Tina Zhang <tina.zhang@intel.com>
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>