RISC-V: Add SBI PMU snapshot definitions

SBI PMU Snapshot function optimizes the number of traps to
higher privilege mode by leveraging a shared memory between the S/VS-mode
and the M/HS mode. Add the definitions for that extension and new error
codes.

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/r/20240420151741.962500-6-atishp@rivosinc.com


Signed-off-by: Anup Patel <anup@brainfault.org>