spirv: handle UniformConstant for OpenCL kernels

spirv: handle UniformConstant for OpenCL kernels

The caller is responsible for setting up the ubo_addr_format value as
contrary to shared and global, it's not controlled by the spirv.

Right now clovers implementation of CL constant memory uses a 24/8 bit format
to encode the buffer index and offset, but that code is dead as all backends
treat constants as global memory to workaround annoying issues within OpenCL.

Maybe that will change, maybe not. But just in case somebody wants to look at
it, add a toggle for this inside vtn.

Signed-off-by: Karol Herbst <kherbst@redhat.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>