drivers/perf: riscv: Reset the counter to hpmevent mapping while starting cpus

Currently, we stop all the counters while a new cpu is brought online.
However, the hpmevent to counter mappings are not reset. The firmware may
have some stale encoding in their mapping structure which may lead to
undesirable results. We have not encountered such scenario though.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/r/20240628-misc_perf_fixes-v4-2-e01cfddcf035@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>