v3d: Bump the maximum texture size to 4k for V3D 4.x.

4.1 and 4.2 both have the same 16k limit, but it I'm seeing GPU hangs in
the CTS at 8k and 16k.  4k at least lets us get one 4k display working.

Cc: mesa-stable@lists.freedesktop.org
(cherry picked from commit 62360e92)