Intgerate Spatz into Snitch Cluster

[DiyouS]

Current known problems:

1. Circulated dependency issue of snitch_pkg.sv: spatz_core need snitch_pkg for the amo_e defines, but it locates in snitch_cluster. We can have it in both repos, and it will work well if snitch_cluster is the top-level, however, it will break down when both repos are dependencies (like in Gwaihir), where we cannot ensure the order of overwriting.
2. Similar problem of riscv_opcodes.sv. Spatz needs one, and snitch_cluster also needs it. Currently, I manually copy the one generated in snitch_cluster to spatz_core and remove it from the Bender.yml in snitch_cluster.
3. Comb loops inside snitch.sv (can be reproduced when setting snitch_cluster_wrapper as module name in spyglass check), not related to Spatz integration

The most appropriate approach is to use snitch_core as a separate dependency/repo, which both spatz_core and snitch_cluster depend on. This could solve all problems of circular dependency. A temporary walkaround only adds one in spatz_core, and uses spatz_core as the dependency of snitch_cluster (like what I did to riscv_opcodes). We may also need to force the update of the generated file from Makefile to ensure it is updated to the version we need.