treewide: Miscellaneous changes to bump dependency in Occamy

[colluca]

Implements several changes to bump the Snitch cluster dependency in Occamy:

• Renames the snitch_cluster Bender target, since this is now used by the DMA and required in Snitch-based systems, to snitch_cluster_wrapper containing the sources which are only needed to simulate/synthesize the snitch_cluster out of context
• Bump non-free repo which was updated with the change above
• Improve Makefile reusability in derived Snitch-based systems
• Remove all DWARF targets since these are unused
• Encode some missing linker prerequisites
• Several changes to improve reuse of Makefiles in derived systems (rename ROOT to SNITCH_ROOT, rename PLATFORM_HEADERS to SNRT_HAL_HDRS, rename snitch_cluster_start.S to snrt.S, make MEMORY_LD overridable)

[fischeti]

LGTM! What's the problem exactly with the overlapping snitch_cluster target in this repo and the DMA?

[colluca]

LGTM! What's the problem exactly with the overlapping snitch_cluster target in this repo and the DMA?

Basically the iDMA uses snitch_cluster as a Bender target for the Snitch DMA sources. We were using the same target for the snitch_cluster_wrapper sources. Occamy, and derived systems, need Snitch's iDMA sources and will thus need to include the snitch_cluster Bender target, but they should not include the wrapper (this failed to compile in Occamy). Thus we need distinct Bender targets.