perf: riscv_pmu{,_sbi}: Miscallenous improvement & fixes

A series of mostly-independent fixes and cleanups for the RISC-V PMU
drivers.

Link: https://lore.kernel.org/lkml/CAAhSdy23vE8+HxU5Jxy2rBMjy3rBTrJt_4sriuROac_sEESSVw@mail.gmail.com/T/#m9de15aef1b65ae6155fa33ea1239578ef463c2a2

* palmer/riscv-pmu:
  RISC-V: Improve SBI definitions
  RISC-V: Move counter info definition to sbi header file
  RISC-V: Fix SBI PMU calls for RV32
  RISC-V: Update user page mapping only once during start
  RISC-V: Fix counter restart during overflow for RV32