zink: 16 bit ALU types
Here's some patches to add support for 16-bit types to Zink.
There's a few things going on here:
- First of all, we need to split up support for 16-bit float and ints, because Vulkan has separate feature-flags for them.
- There's a bugfix for nir_lower_tex that only seems to trigger with 16-bit types.
- A few minor fixes to the nir-to-spirv code
- And finally the juicy bits.