ANDROID: virtio-gpu api: create guest handle

This feature allows the creation of OS-specific handles from guest
memory.  A handle is typically an dmabuf, Zircon handle, or Win32
descriptor.  Right now, only udmabuf on Linux has this capability,
but VIRTIO_GPU_BLOB_FLAG_CREATE_GUEST_UDMABUF seemed OS-specific
given the goals of the virtio initiative.

It only works with BLOB_MEM_GUEST, of course.

We can also name it some like VIRTIO_GPU_BLOB_FLAG_HANDLE_FROM_GUEST
*shrugs*.

Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>

BUG: 173630595
TEST: boot VM

Change-Id: I5686e6db37f7ee9d5ffca4d38f3711468a48b7ea