Updated a PMPZca coverpoint

I pulled the missing tests from draft PR #699 and compiled them. Although the tests were failing due to Sail and Spike mismatches, the tests themselves are correct. I ran the binaries on both Wally and Imperas to collect coverage.

However, a few bins in a cross were not being hit. Specifically, the crosses of c.lwsp and c.ldsp with at_region were uncovered because at_region depends on (ins.current.rs1_val + ins.current.imm). For c.lwsp and c.ldsp, we can’t verify the accessed address using rs1_val as per their encoding, which explains the missed coverage.

Now, if the PR gets merged, we'll have the 100% coverage for both XLEN.

Covergroup                                             Metric       Goal       Bins    Status               
 TYPE PMPM_cg                                          100.00%        100          -    Covered
 TYPE PMPU_cg                                          100.00%        100          -    Covered
 TYPE PMPS_cg                                          100.00%        100          -    Covered
 TYPE PMPF_cg                                          100.00%        100          -    Covered
 TYPE PMPZaamo_cg                                      100.00%        100          -    Covered
 TYPE PMPZalrsc_cg                                     100.00%        100          -    Covered
 TYPE PMPZca_cg                                        100.00%        100          -    Covered
 TYPE PMPZicbo_cg                                      100.00%        100          -    Covered