spirv: Use nir_var_mem_constant for UniformConstant data in CL

For now, we leave the constant_as_global option intact and get rid of
the UBO path which no one upstream is using today.

Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6379>
4 files changed