target/riscv/cpu.c: move 'mimpid' to riscv_cpu_properties[]

target/riscv/cpu.c: move 'mimpid' to riscv_cpu_properties[]

Keep all class properties in riscv_cpu_properties[].

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Tested-by: Vladimir Isaev <vladimir.isaev@syntacore.com>
tested-by tags added, rebased with Alistair's riscv-to-apply.next.
Message-ID: <20240112140201.127083-8-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>