[topgen] Create the RAL only, no other files
[topgen] Create the RAL only, no other files

When asking topgen to create the chip-level RAL we only need
two files: `chip_ral_pkg.core` and `chip_ral_pkg.sv`. Before this patch,
however, we additionally created a fair amount of RTL, DV and
documentation files in the output directory.

These files didn't do much harm before, but are doing more harm now that
ipgen is getting used more: as part of topgen, we also create IP
instances (including their core files), which end up in the output
directory. This effectively gives us multiple copies of the generated IP
blocks, one copy in `hw/top_earlgrey/ip_autogen`, and another copy
produced at build time (by ralgen calling topgen) in the FuseSoC build
directory. That doesn't sound like it'll go well, and it turns out: it
doesn't (the errors are obscure).

This beautiful commit ensures that topgen only produces `chip_ral_pkg.core`
and `chip_ral_pkg.sv` when asked to produce the chip-level RAL. Since we
still need all the other files produced by topgen to actually produce
the RAL later in time, we simply let topgen continue to produce and use
those files, and delete them in the end.

Fixes #7857

Signed-off-by: Philipp Wagner <5a4b10454c30419e54a1570be358a516ff84bb63@lowrisc.org>

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