target/riscv: pmp: Clear pmp/smepmp bits on reset

target/riscv: pmp: Clear pmp/smepmp bits on reset

As per the Priv and Smepmp specifications, certain bits such as the 'L'
bit of pmp entries and mseccfg.MML can only be cleared upon reset and it
is necessary to do so to allow 'M' mode firmware to correctly reinitialize
the pmp/smpemp state across reboots. As required by the spec, also clear
the 'A' field of pmp entries.

Signed-off-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20231019065644.1431798-1-mchitale@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>