drm/i915/gvt/kvmgt: fill info for ROM/VGA region

Both ROM/VGA region are not supported for vGPU in GVT. But if the device
model want to get those region, we should return the correct information
but not leave the structure with random data. Change to same operation
of BAR3-BAR5 which are also not supported by vGPU.

Refer to function @intel_vgpu_rw.

Signed-off-by: Pei Zhang <pei.zhang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>