drm/i915/gvt: Revert "drm/i915/gvt: Refine the snapshort range of I915 MCHBAR...

drm/i915/gvt: Revert "drm/i915/gvt: Refine the snapshort range of I915 MCHBAR to optimize gvt-g boot time"

This reverts commit f74a6d9a.

BXT needs to access 0x141000-0x1417ff register to obtain the dram info.
But after the snapshot range of I915_MCHBAR is refined in f74a6d9a,
it only initializes the range of 0x144000-0x147fff for VGPU and then
causes that the guest GPU can't get the initialized value for dram
detection on BXT.

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>