freedreno/layout: layout simplifications and pitch from level 0 pitch

This updates a3xx/a4xx/a5xx to fix the fetchsize to PITCHALIGN (called MINLINEOFFSET by the a3xx docs), and some simplifications to make things more like a6xx. Also similar simplifications for a2xx layout code.

The pitch can always be determined using a simple calculation from the base level pitch, so don't pre-calculate a pitch for each mipmap level.

This passes CI but a3xx/a5xx don't test with tiling enabled. a5xx should be fine but a3xx seemed to have already broken tiling, so I'm not sure about it..

Ended up as a bit of a mega-commit doing a couple different things (but all related to getting rid of pitch from fdl_slice), hopefully not too bad to review..