intel/compiler: Get rid of struct gen_disasm

intel/compiler: Get rid of struct gen_disasm

It's just a container around a devinfo.  The one useful purpose it did
serve is that gen_disasm_create initialized the compaction table
singletons.  Now that those no longer exist, this isn't necessary.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6244>