drm/virtio: Extend blob UAPI with deferred-mapping hinting

drm/virtio: Extend blob UAPI with deferred-mapping hinting

If userspace never maps GEM object, then BO wastes hostmem space
because VirtIO-GPU driver maps VRAM BO at the BO's creating time.

Make mappings on-demand by adding new RESOURCE_CREATE_BLOB IOCTL/UAPI
hinting flag telling that host mapping should be deferred until first
mapping is made when the flag is set by userspace.

Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Link: https://patch.msgid.link/20260501000043.2483678-1-dmitry.osipenko@collabora.com