target/riscv: Don't assume PMU counters are continuous

target/riscv: Don't assume PMU counters are continuous

Check the PMU available bitmask when checking if a counter is valid
rather than comparing the index against the number of PMUs.

Signed-off-by: Rob Bradford <rbradford@rivosinc.com>
Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Message-ID: <20231031154000.18134-3-rbradford@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>