target/riscv: pmp: Ignore writes when RW=01

target/riscv: pmp: Ignore writes when RW=01

As per the Priv spec: "The R, W, and X fields form a collective WARL
field for which the combinations with R=0 and W=1 are reserved."
However currently such writes are not ignored as ought to be. The
combinations with RW=01 are allowed only when the Smepmp extension
is enabled and mseccfg.MML is set.

Signed-off-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20231019065705.1431868-1-mchitale@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>