freedreno/a5xx: Add support for clip distances and use them for userclip.

A little low-stakes RE effort as I unwind from fighting CI all day. Comes from diffing dEQP-VK.clipping.user_defined.clip_distance.vert.* on the blob and comparing to a6xx behavior. (My blob doesn't do tess, so if there are equivalent tess fields for some of these, I didn't find them)