[fpv] prim and top-level IP improvements

[vogelpi]

Description

For Earlgrey-PROD.M4 and as part of #22721 @rswarbrick managed to substantially improve FPV pass rates and coverage for the prim and top-level IP regressions:

• https://reports.opentitan.org/hw/top_earlgrey/formal/ip/summary/latest/report.html
• https://reports.opentitan.org/hw/top_earlgrey/formal/prim/summary/latest/report.html

As documented by @rswarbrick here, the following two things remain to be resolved for future releases:

• Improving pass rates for prim_fifo_sync_fpv and prim_fifo_async_sram_adapter_fpv. These might need some tooling workarounds.
• Improving coverage numbers for pinmux and rv_plic. Most existing gaps are due to COIs of SVAs not touching the signals of interest, in particular inside u_reg.

Both these items are of lower priority but if we decide to investigate this further, this issue can serve as a starting point / reference to previous work.

[rswarbrick]

The pass rates described as the first item here should get to 100% with the changes in #24432 and #24433.