panfrost: fix sampler_count and unbind samplers in bind_sampler_states

Details in commit message. Change was done in the same way as the freedreno code:

https://gitlab.freedesktop.org/mesa/mesa/-/blob/a0991c7c794da39bf1a4b5fb5484b77afde200cc/src/gallium/drivers/freedreno/freedreno_texture.c#L51

Changes was tested on one game with Gallium Nine. Before:

After changes: