target/riscv: csr: Remove redundant check in fp csr read/write routines

target/riscv: csr: Remove redundant check in fp csr read/write routines

The following check:

    if (!env->debugger && !riscv_cpu_fp_enabled(env)) {
        return -RISCV_EXCP_ILLEGAL_INST;
    }

is redundant in fflags/frm/fcsr read/write routines, as the check was
already done in fs().

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20210627120604.11116-1-bmeng.cn@gmail.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>