target/riscv/cpu.c: remove cpu->cfg.vlen

target/riscv/cpu.c: remove cpu->cfg.vlen

There is no need to keep both 'vlen' and 'vlenb'. All existing code
that requires 'vlen' is retrieving it via 'vlenb << 3'.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20240122161107.26737-14-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>