target/riscv: Mask out upper sscofpmf bits during validation

target/riscv: Mask out upper sscofpmf bits during validation

As per the ISA definition, the upper 8 bits in hpmevent are defined
by Sscofpmf for privilege mode filtering and overflow bits while the
lower 56 bits are desginated for platform specific hpmevent values.
For the reset case, mhpmevent value should have zero in lower 56 bits.
Software may set the OF bit to indicate disable interrupt.

Ensure that correct value is checked after masking while clearing the
event encodings.

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: <20250206-pmu_minor_fixes-v2-2-1bb0f4aeb8b4@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>