intel/tools: Don't hardcode notification register

intel/tools: Don't hardcode notification register

Previously we parsed a src non-terminal but did nothing with it. Since
the WAIT instruction is kind of weird, in that you have to give it the
same notification subregister for both destination and source, and it
always has an exec size of 1, let's parse a destination instead of a
source. This way, we can parse a writemask rather than a swizzle in
align16 mode, and easily convert the writemask to a swizzle to create
the source register.

Reviewed-by: Sagar Ghuge <sagar.ghuge@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5956>