r600g: fix texture array filtering

r600g: fix texture array filtering

This fixes piglit/fbo-generatemipmap-array.

It looks like SQ_TEX_SAMPLER_WORD0_0.TEX_ARRAY_OVERRIDE should be set
for array textures in order to disable filtering between slices,
which adds a dependency between sampler views and sampler states.

This patch reworks sampler state updates such that they are postponed until
draw time. TEX_ARRAY_OVERRIDE is updated according to bound sampler views.

This also consolidates setting the texture state between vertex and
pixel shaders.