vfio: Disable igd stolen memory
vfio: Disable igd stolen memory

igd stolen memory isn't a standard pci resource, so guest couldn't
access it. Once guest i915 driver see its size is zero, i915 won't use
it. Here sotlen memory's size register PciCfg 0x51 is forced to zero.

BUG=chromium:992270
TEST=crosvm run --vfio=/sys/devices/pci0000:00/0000:00:02.0, pass
through host igd into linux guest. The physical local display lightup and show linux desktop.

Change-Id: I1a0a6edda5d92d32307ea8025ef96677ca62c125
Signed-off-by: Xiong Zhang <887154684953c1d7bc9f653d05b20c8de98c15bc@intel.corp-partner.google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/1688368
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm