turnip: Add support for uniform texel buffers.

turnip: Add support for uniform texel buffers.

Pretty straightforward: Port texture descriptor code from freedreno, fill
in alignment limits from closed vk, and tu_cmd_buffer.c was already
uploading the texture descriptor.

This doesn't implement storage texel buffers (required in the compute
pipeline) yet, since those will need an IBO descriptor for the store path.
Still, making the load path be connected to the texture descriptor won't
hurt.

Part of #2237

Fixes dEQP-VK.binding_model.shader_access.primary_cmd_buf.uniform_texel_buffer.*

Reviewed-by: Jonathan Marek <jonathan@marek.ca>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3522>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3522>