Inconsistent PMP tests' names

[marcfedorow]

riscv-test-suite/rv32i_m/pmp32/PMP-CFG-reg.S
riscv-test-suite/rv32i_m/pmp32/pmp-NA4-R-priority-level-2.S
riscv-test-suite/rv64i_m/pmp64/pmp64-CFG-reg.S
These tests are hard to filter using their names
(Check must be case insensitive or use the full path)

To be consistent with other folders, the following should be done:

• Do not indicate XLEN other than in rvXLENi_m folder name
• Do not use uppercase (or use it consistently)

I.e., these are the good paths/names:
riscv-test-suite/rv32i_m/pmp/pmp-cfg-reg.S
riscv-test-suite/rv64i_m/pmp/pmp-cfg-reg.S