target/riscv: remove cpu->cfg.ext_m

target/riscv: remove cpu->cfg.ext_m

Create a new "m" RISCVCPUMisaExtConfig property that will update
env->misa_ext* with RVM. Instances of cpu->cfg.ext_m and similar are
replaced with riscv_has_ext(env, RVM).

Remove the old "m" property and 'ext_m' from RISCVCPUConfig.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20230406180351.570807-12-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>