target/riscv: Implement privilege mode filtering for cycle/instret

target/riscv: Implement privilege mode filtering for cycle/instret

Privilege mode filtering can also be emulated for cycle/instret by
tracking host_ticks/icount during each privilege mode switch. This
patch implements that for both cycle/instret and mhpmcounters. The
first one requires Smcntrpmf while the other one requires Sscofpmf
to be enabled.

The cycle/instret are still computed using host ticks when icount
is not enabled. Otherwise, they are computed using raw icount which
is more accurate in icount mode.

Co-Developed-by: Rajnesh Kanwal <rkanwal@rivosinc.com>
Signed-off-by: Rajnesh Kanwal <rkanwal@rivosinc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Message-ID: <20240711-smcntrpmf_v7-v8-7-b7c38ae7b263@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>