perf: RISC-V: exclude invalid pmu counters from SBI calls

SBI firmware may not provide information for some counters in response
to SBI_EXT_PMU_COUNTER_GET_INFO call. Exclude such counters from the
subsequent SBI requests. For this purpose use global mask to keep track
of fully specified counters.

Signed-off-by: Sergey Matyukevich <sergey.matyukevich@syntacore.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/r/20220830155306.301714-3-geomatsi@gmail.com


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>