freedreno/a3xx: fix 3d texture layout

freedreno/a3xx: fix 3d texture layout

The SZ2 field contains the layer size of a lower miplevel. It only
contains 4 bits, which limits the maximum layer size it can describe. In
situations where the next miplevel would be too big, the hardware
appears to keep minifying the size until it hits one of that size.
Unfortunately the hardware's ideas about sizes can differ from
freedreno's which can still lead to issues. Minimize those by stopping
to minify as soon as possible.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: "10.4 10.5" <mesa-stable@lists.freedesktop.org>