broadcom/vc4: Keep pipe_sampler_view->texture matching the original texture.

broadcom/vc4: Keep pipe_sampler_view->texture matching the original texture.

I was overwriting view->texture with the shadow resource when we need to
do shadow copies (retiling or baselevel rebase), but that tripped up some
critical new sanity checking in state_tracker (making sure that stObj->pt
hasn't changed from view->texture through TexImage-related paths).

To avoid that, move the shadow resource to the vc4_sampler_view struct.

Fixes: f0ecd36ef8e1 ("st/mesa: add an entirely separate codepath for setting up buffer views")