tcg/riscv: Fix branch range checks

tcg/riscv: Fix branch range checks

The offset even checks were folded into the range check incorrectly.
By offsetting by 1, and not decrementing the width, we silently
allowed out of range branches.

Assert that the offset is always even instead.  Move tcg_out_goto
down into the CONFIG_SOFTMMU block so that it is not unused.

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>