target/riscv: Split RISCVCPUConfig declarations from cpu.h into cpu_cfg.h

target/riscv: Split RISCVCPUConfig declarations from cpu.h into cpu_cfg.h

Split RISCVCPUConfig declarations to prepare for passing it to disas.

Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-Id: <20230523093539.203909-3-liweiwei@iscas.ac.cn>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>