[RISCV][NFC] Use TableGen 'foreach' to simplify repetitive CSR definitions

Make the definitions of hpmcounter3-hpmcounter31,
hpmcounter3h-hpmcounter31h, mhpmcounter3-mhpmcounter31,
mhpmcounter3h-mhpmcounter31h, pmpaddr0-pmpaddr63, mhpmevent3-31, and
pmpcfg0-15 substantially less repetitive using a foreach loop.

Differential Revision: https://reviews.llvm.org/D117227