target/riscv: Fix priority of csr related check in riscv_csrrw_check

target/riscv: Fix priority of csr related check in riscv_csrrw_check

Normally, riscv_csrrw_check is called when executing Zicsr instructions.
And we can only do access control for existed CSRs. So the priority of
CSR related check, from highest to lowest, should be as follows:
1) check whether Zicsr is supported: raise RISCV_EXCP_ILLEGAL_INST if not
2) check whether csr is existed: raise RISCV_EXCP_ILLEGAL_INST if not
3) do access control: raise RISCV_EXCP_ILLEGAL_INST or RISCV_EXCP_VIRT_
INSTRUCTION_FAULT if not allowed

The predicates contain parts of function of both 2) and 3), So they need
to be placed in the middle of riscv_csrrw_check

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: <20220803123652.3700-1-liweiwei@iscas.ac.cn>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>