[rv_dm] Address Verilator lint warnings

[rswarbrick]

Description

The nightly lint check for rv_dm contains 5 warnings.

It looks like 4 of these are width bugs in the vendored code. No big deal, but probably worth waiving in a .vlt file. There's also an UNOPTFLAT warning about tlul_lc_gate.sv, which we wrote. Address it.

See https://reports.opentitan.org/hw/ip/rv_dm/lint/verilator/latest/report.html for the latest report.

[rswarbrick]

The two PRs linked in above should fix this. I don't think I know how to use PR links to say "please close this issue when both PRs have been merged", so we might have to do it manually... :-)

[rswarbrick]

The remaining portion of this is fixed by #22486 (but I don't seem to be able to create the links through GitHub that would put this in the "development" box on the right)

[andreaskurth]

Closing as completed by #21736 and #22486.