target/riscv: check 'I' and 'E' after checking 'G' in riscv_cpu_realize

target/riscv: check 'I' and 'E' after checking 'G' in riscv_cpu_realize

 - setting ext_g will implicitly set ext_i

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>
Message-Id: <20220518012611.6772-1-liweiwei@iscas.ac.cn>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>