drm/vmwgfx: Make the driver work without the dummy resources

In commit 18025378

 ("drm/ttm: stop allocating dummy resources during BO creation")
ttm stopped allocating dummy resources but vmwgfx was never ported to
handle it. Make the driver treat null resources as initial creation and
port code to handle null resources in general.

Fixes kernel oops'es on boot with vmwgfx.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Fixes: 18025378

 ("drm/ttm: stop allocating dummy resources during BO creation")
Cc: Christian König <christian.koenig@amd.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Nirmoy Das <nirmoy.das@intel.com>
Cc: Christian Koenig <christian.koenig@amd.com>
Cc: Huang Rui <ray.huang@amd.com>
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230210023437.2214816-1-zack@kde.org